doc/src/sgml/catalogs.sgml

<!-- doc/src/sgml/catalogs.sgml -->
<!--
 Documentation of the system catalogs, directed toward PostgreSQL developers
 -->

<chapter id="catalogs">
 <title>System Catalogs</title>

  <para>
   The system catalogs are the place where a relational database
   management system stores schema metadata, such as information about
   tables and columns, and internal bookkeeping information.
   <productname>PostgreSQL</productname>'s system catalogs are regular
   tables.  You can drop and recreate the tables, add columns, insert
   and update values, and severely mess up your system that way.
   Normally, one should not change the system catalogs by hand, there
   are normally SQL commands to do that.  (For example, <command>CREATE
   DATABASE</command> inserts a row into the
   <structname>pg_database</structname> catalog &mdash; and actually
   creates the database on disk.)  There are some exceptions for
   particularly esoteric operations, but many of those have been made
   available as SQL commands over time, and so the need for direct manipulation
   of the system catalogs is ever decreasing.
  </para>

 <sect1 id="catalogs-overview">
  <title>Overview</title>

  <para>
   <xref linkend="catalog-table"/> lists the system catalogs.
   More detailed documentation of each catalog follows below.
  </para>

  <para>
   Most system catalogs are copied from the template database during
   database creation and are thereafter database-specific. A few
   catalogs are physically shared across all databases in a cluster;
   these are noted in the descriptions of the individual catalogs.
  </para>

  <table id="catalog-table">
   <title>System Catalogs</title>

   <tgroup cols="2">
    <thead>
     <row>
      <entry>Catalog Name</entry>
      <entry>Purpose</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><link linkend="catalog-pg-aggregate"><structname>pg_aggregate</structname></link></entry>
      <entry>aggregate functions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-am"><structname>pg_am</structname></link></entry>
      <entry>relation access methods</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-amop"><structname>pg_amop</structname></link></entry>
      <entry>access method operators</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-amproc"><structname>pg_amproc</structname></link></entry>
      <entry>access method support functions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-attrdef"><structname>pg_attrdef</structname></link></entry>
      <entry>column default values</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link></entry>
      <entry>table columns (<quote>attributes</quote>)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link></entry>
      <entry>authorization identifiers (roles)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link></entry>
      <entry>authorization identifier membership relationships</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-cast"><structname>pg_cast</structname></link></entry>
      <entry>casts (data type conversions)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-class"><structname>pg_class</structname></link></entry>
      <entry>tables, indexes, sequences, views (<quote>relations</quote>)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-collation"><structname>pg_collation</structname></link></entry>
      <entry>collations (locale information)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link></entry>
      <entry>check constraints, unique constraints, primary key constraints, foreign key constraints</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-conversion"><structname>pg_conversion</structname></link></entry>
      <entry>encoding conversion information</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-database"><structname>pg_database</structname></link></entry>
      <entry>databases within this database cluster</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-db-role-setting"><structname>pg_db_role_setting</structname></link></entry>
      <entry>per-role and per-database settings</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-default-acl"><structname>pg_default_acl</structname></link></entry>
      <entry>default privileges for object types</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-depend"><structname>pg_depend</structname></link></entry>
      <entry>dependencies between database objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-description"><structname>pg_description</structname></link></entry>
      <entry>descriptions or comments on database objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-enum"><structname>pg_enum</structname></link></entry>
      <entry>enum label and value definitions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-event-trigger"><structname>pg_event_trigger</structname></link></entry>
      <entry>event triggers</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-extension"><structname>pg_extension</structname></link></entry>
      <entry>installed extensions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-foreign-data-wrapper"><structname>pg_foreign_data_wrapper</structname></link></entry>
      <entry>foreign-data wrapper definitions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-foreign-server"><structname>pg_foreign_server</structname></link></entry>
      <entry>foreign server definitions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-foreign-table"><structname>pg_foreign_table</structname></link></entry>
      <entry>additional foreign table information</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-index"><structname>pg_index</structname></link></entry>
      <entry>additional index information</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-inherits"><structname>pg_inherits</structname></link></entry>
      <entry>table inheritance hierarchy</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-init-privs"><structname>pg_init_privs</structname></link></entry>
      <entry>object initial privileges</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-language"><structname>pg_language</structname></link></entry>
      <entry>languages for writing functions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-largeobject"><structname>pg_largeobject</structname></link></entry>
      <entry>data pages for large objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-largeobject-metadata"><structname>pg_largeobject_metadata</structname></link></entry>
      <entry>metadata for large objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link></entry>
      <entry>schemas</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link></entry>
      <entry>access method operator classes</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link></entry>
      <entry>operators</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link></entry>
      <entry>access method operator families</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-partitioned-table"><structname>pg_partitioned_table</structname></link></entry>
      <entry>information about partition key of tables</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-policy"><structname>pg_policy</structname></link></entry>
      <entry>row-security policies</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link></entry>
      <entry>functions and procedures</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-publication"><structname>pg_publication</structname></link></entry>
      <entry>publications for logical replication</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-publication-rel"><structname>pg_publication_rel</structname></link></entry>
      <entry>relation to publication mapping</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-range"><structname>pg_range</structname></link></entry>
      <entry>information about range types</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-replication-origin"><structname>pg_replication_origin</structname></link></entry>
      <entry>registered replication origins</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link></entry>
      <entry>query rewrite rules</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-seclabel"><structname>pg_seclabel</structname></link></entry>
      <entry>security labels on database objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-sequence"><structname>pg_sequence</structname></link></entry>
      <entry>information about sequences</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link></entry>
      <entry>dependencies on shared objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link></entry>
      <entry>comments on shared objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-shseclabel"><structname>pg_shseclabel</structname></link></entry>
      <entry>security labels on shared database objects</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link></entry>
      <entry>planner statistics</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link></entry>
      <entry>extended planner statistics (definition)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link></entry>
      <entry>extended planner statistics (built statistics)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-subscription"><structname>pg_subscription</structname></link></entry>
      <entry>logical replication subscriptions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-subscription-rel"><structname>pg_subscription_rel</structname></link></entry>
      <entry>relation state for subscriptions</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link></entry>
      <entry>tablespaces within this database cluster</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-transform"><structname>pg_transform</structname></link></entry>
      <entry>transforms (data type to procedural language conversions)</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link></entry>
      <entry>triggers</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-ts-config"><structname>pg_ts_config</structname></link></entry>
      <entry>text search configurations</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-ts-config-map"><structname>pg_ts_config_map</structname></link></entry>
      <entry>text search configurations' token mappings</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-ts-dict"><structname>pg_ts_dict</structname></link></entry>
      <entry>text search dictionaries</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-ts-parser"><structname>pg_ts_parser</structname></link></entry>
      <entry>text search parsers</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-ts-template"><structname>pg_ts_template</structname></link></entry>
      <entry>text search templates</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-type"><structname>pg_type</structname></link></entry>
      <entry>data types</entry>
     </row>

     <row>
      <entry><link linkend="catalog-pg-user-mapping"><structname>pg_user_mapping</structname></link></entry>
      <entry>mappings of users to foreign servers</entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-aggregate">
  <title><structname>pg_aggregate</structname></title>

  <indexterm zone="catalog-pg-aggregate">
   <primary>pg_aggregate</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_aggregate</structname> stores information about
   aggregate functions.  An aggregate function is a function that
   operates on a set of values (typically one column from each row
   that matches a query condition) and returns a single value computed
   from all these values.  Typical aggregate functions are
   <function>sum</function>, <function>count</function>, and
   <function>max</function>.  Each entry in
   <structname>pg_aggregate</structname> is an extension of an entry
   in <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.
   The <structname>pg_proc</structname> entry carries the aggregate's name,
   input and output data types, and other information that is similar to
   ordinary functions.
  </para>

  <table>
   <title><structname>pg_aggregate</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggfnoid</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       <structname>pg_proc</structname> OID of the aggregate function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggkind</structfield> <type>char</type>
      </para>
      <para>
       Aggregate kind:
       <literal>n</literal> for <quote>normal</quote> aggregates,
       <literal>o</literal> for <quote>ordered-set</quote> aggregates, or
       <literal>h</literal> for <quote>hypothetical-set</quote> aggregates
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggnumdirectargs</structfield> <type>int2</type>
      </para>
      <para>
       Number of direct (non-aggregated) arguments of an ordered-set or
       hypothetical-set aggregate, counting a variadic array as one argument.
       If equal to <structfield>pronargs</structfield>, the aggregate must be variadic
       and the variadic array describes the aggregated arguments as well as
       the final direct arguments.
       Always zero for normal aggregates.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggtransfn</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Transition function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggfinalfn</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Final function (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggcombinefn</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Combine function (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggserialfn</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Serialization function (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggdeserialfn</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Deserialization function (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggmtransfn</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Forward transition function for moving-aggregate mode (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggminvtransfn</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Inverse transition function for moving-aggregate mode (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggmfinalfn</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Final function for moving-aggregate mode (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggfinalextra</structfield> <type>bool</type>
      </para>
      <para>
       True to pass extra dummy arguments to <structfield>aggfinalfn</structfield>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggmfinalextra</structfield> <type>bool</type>
      </para>
      <para>
       True to pass extra dummy arguments to <structfield>aggmfinalfn</structfield>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggfinalmodify</structfield> <type>char</type>
      </para>
      <para>
       Whether <structfield>aggfinalfn</structfield> modifies the
       transition state value:
       <literal>r</literal> if it is read-only,
       <literal>s</literal> if the <structfield>aggtransfn</structfield>
       cannot be applied after the <structfield>aggfinalfn</structfield>, or
       <literal>w</literal> if it writes on the value
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggmfinalmodify</structfield> <type>char</type>
      </para>
      <para>
       Like <structfield>aggfinalmodify</structfield>, but for
       the <structfield>aggmfinalfn</structfield>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggsortop</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Associated sort operator (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggtranstype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Data type of the aggregate function's internal transition (state) data
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggtransspace</structfield> <type>int4</type>
      </para>
      <para>
       Approximate average size (in bytes) of the transition state
       data, or zero to use a default estimate
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggmtranstype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Data type of the aggregate function's internal transition (state)
       data for moving-aggregate mode (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggmtransspace</structfield> <type>int4</type>
      </para>
      <para>
       Approximate average size (in bytes) of the transition state data
       for moving-aggregate mode, or zero to use a default estimate
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>agginitval</structfield> <type>text</type>
      </para>
      <para>
       The initial value of the transition state.  This is a text
       field containing the initial value in its external string
       representation.  If this field is null, the transition state
       value starts out null.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>aggminitval</structfield> <type>text</type>
      </para>
      <para>
       The initial value of the transition state for moving-aggregate mode.
       This is a text field containing the initial value in its external
       string representation.  If this field is null, the transition state
       value starts out null.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   New aggregate functions are registered with the <link
   linkend="sql-createaggregate"><command>CREATE AGGREGATE</command></link>
   command.  See <xref linkend="xaggr"/> for more information about
   writing aggregate functions and the meaning of the transition
   functions, etc.
  </para>

 </sect1>


 <sect1 id="catalog-pg-am">
  <title><structname>pg_am</structname></title>

  <indexterm zone="catalog-pg-am">
   <primary>pg_am</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_am</structname> stores information about
   relation access methods.  There is one row for each access method supported
   by the system.
   Currently, only tables and indexes have access methods. The requirements for table
   and index access methods are discussed in detail in <xref linkend="tableam"/> and
   <xref linkend="indexam"/> respectively.
  </para>

  <table>
   <title><structname>pg_am</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amname</structfield> <type>name</type>
      </para>
      <para>
       Name of the access method
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amhandler</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of a handler function that is responsible for supplying information
       about the access method
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amtype</structfield> <type>char</type>
      </para>
      <para>
       <literal>t</literal> = table (including materialized views),
       <literal>i</literal> = index.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <note>
   <para>
    Before <productname>PostgreSQL</productname> 9.6, <structname>pg_am</structname>
    contained many additional columns representing properties of index access
    methods.  That data is now only directly visible at the C code level.
    However, <function>pg_index_column_has_property()</function> and related
    functions have been added to allow SQL queries to inspect index access
    method properties; see <xref linkend="functions-info-catalog-table"/>.
   </para>
  </note>

 </sect1>


 <sect1 id="catalog-pg-amop">
  <title><structname>pg_amop</structname></title>

  <indexterm zone="catalog-pg-amop">
   <primary>pg_amop</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_amop</structname> stores information about
   operators associated with access method operator families.  There is one
   row for each operator that is a member of an operator family.  A family
   member can be either a <firstterm>search</firstterm> operator or an
   <firstterm>ordering</firstterm> operator.  An operator
   can appear in more than one family, but cannot appear in more than one
   search position nor more than one ordering position within a family.
   (It is allowed, though unlikely, for an operator to be used for both
   search and ordering purposes.)
  </para>

  <table>
   <title><structname>pg_amop</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amopfamily</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The operator family this entry is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amoplefttype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Left-hand input data type of operator
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amoprighttype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Right-hand input data type of operator
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amopstrategy</structfield> <type>int2</type>
      </para>
      <para>
       Operator strategy number
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amoppurpose</structfield> <type>char</type>
      </para>
      <para>
       Operator purpose, either <literal>s</literal> for search or
       <literal>o</literal> for ordering
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amopopr</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the operator
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amopmethod</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-am"><structname>pg_am</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Index access method operator family is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amopsortfamily</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The B-tree operator family this entry sorts according to, if an
       ordering operator; zero if a search operator
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   A <quote>search</quote> operator entry indicates that an index of this operator
   family can be searched to find all rows satisfying
   <literal>WHERE</literal>
   <replaceable>indexed_column</replaceable>
   <replaceable>operator</replaceable>
   <replaceable>constant</replaceable>.
   Obviously, such an operator must return <type>boolean</type>, and its left-hand input
   type must match the index's column data type.
  </para>

  <para>
   An <quote>ordering</quote> operator entry indicates that an index of this
   operator family can be scanned to return rows in the order represented by
   <literal>ORDER BY</literal>
   <replaceable>indexed_column</replaceable>
   <replaceable>operator</replaceable>
   <replaceable>constant</replaceable>.
   Such an operator could return any sortable data type, though again
   its left-hand input type must match the index's column data type.
   The exact semantics of the <literal>ORDER BY</literal> are specified by the
   <structfield>amopsortfamily</structfield> column, which must reference
   a B-tree operator family for the operator's result type.
  </para>

  <note>
   <para>
    At present, it's assumed that the sort order for an ordering operator
    is the default for the referenced operator family, i.e., <literal>ASC NULLS
    LAST</literal>.  This might someday be relaxed by adding additional columns
    to specify sort options explicitly.
   </para>
  </note>

  <para>
   An entry's <structfield>amopmethod</structfield> must match the
   <structfield>opfmethod</structfield> of its containing operator family (including
   <structfield>amopmethod</structfield> here is an intentional denormalization of the
   catalog structure for performance reasons).  Also,
   <structfield>amoplefttype</structfield> and <structfield>amoprighttype</structfield> must match
   the <structfield>oprleft</structfield> and <structfield>oprright</structfield> fields of the
   referenced <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link> entry.
  </para>

 </sect1>


 <sect1 id="catalog-pg-amproc">
  <title><structname>pg_amproc</structname></title>

  <indexterm zone="catalog-pg-amproc">
   <primary>pg_amproc</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_amproc</structname> stores information about
   support functions associated with access method operator families.  There
   is one row for each support function belonging to an operator family.
  </para>

  <table>
   <title><structname>pg_amproc</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amprocfamily</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The operator family this entry is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amproclefttype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Left-hand input data type of associated operator
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amprocrighttype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Right-hand input data type of associated operator
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amprocnum</structfield> <type>int2</type>
      </para>
      <para>
       Support function number
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>amproc</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the function
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The usual interpretation of the
   <structfield>amproclefttype</structfield> and <structfield>amprocrighttype</structfield> fields
   is that they identify the left and right input types of the operator(s)
   that a particular support function supports.  For some access methods
   these match the input data type(s) of the support function itself, for
   others not.  There is a notion of <quote>default</quote> support functions for
   an index, which are those with <structfield>amproclefttype</structfield> and
   <structfield>amprocrighttype</structfield> both equal to the index operator class's
   <structfield>opcintype</structfield>.
  </para>

 </sect1>


 <sect1 id="catalog-pg-attrdef">
  <title><structname>pg_attrdef</structname></title>

  <indexterm zone="catalog-pg-attrdef">
   <primary>pg_attrdef</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_attrdef</structname> stores column default
   values.  The main information about columns is stored in
   <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.
   Only columns for which a default value has been explicitly set will have
   an entry here.
  </para>

  <table>
   <title><structname>pg_attrdef</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>adrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The table this column belongs to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>adnum</structfield> <type>int2</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attnum</structfield>)
      </para>
      <para>
       The number of the column
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>adbin</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       The column default value, in <function>nodeToString()</function>
       representation.  Use <literal>pg_get_expr(adbin, adrelid)</literal> to
       convert it to an SQL expression.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-attribute">
  <title><structname>pg_attribute</structname></title>

  <indexterm zone="catalog-pg-attribute">
   <primary>pg_attribute</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_attribute</structname> stores information about
   table columns.  There will be exactly one
   <structname>pg_attribute</structname> row for every column in every
   table in the database.  (There will also be attribute entries for
   indexes, and indeed all objects that have
   <link linkend="catalog-pg-class"><structname>pg_class</structname></link>
   entries.)
  </para>

  <para>
   The term attribute is equivalent to column and is used for
   historical reasons.
  </para>

  <table>
   <title><structname>pg_attribute</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The table this column belongs to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attname</structfield> <type>name</type>
      </para>
      <para>
       The column name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>atttypid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The data type of this column (zero for a dropped column)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attstattarget</structfield> <type>int4</type>
      </para>
      <para>
       <structfield>attstattarget</structfield> controls the level of detail
       of statistics accumulated for this column by
       <link linkend="sql-analyze"><command>ANALYZE</command></link>.
       A zero value indicates that no statistics should be collected.
       A negative value says to use the system default statistics target.
       The exact meaning of positive values is data type-dependent.
       For scalar data types, <structfield>attstattarget</structfield>
       is both the target number of <quote>most common values</quote>
       to collect, and the target number of histogram bins to create.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attlen</structfield> <type>int2</type>
      </para>
      <para>
       A copy of <literal>pg_type.typlen</literal> of this column's
       type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attnum</structfield> <type>int2</type>
      </para>
      <para>
       The number of the column.  Ordinary columns are numbered from 1
       up.  System columns, such as <structfield>ctid</structfield>,
       have (arbitrary) negative numbers.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attndims</structfield> <type>int4</type>
      </para>
      <para>
       Number of dimensions, if the column is an array type; otherwise 0.
       (Presently, the number of dimensions of an array is not enforced,
       so any nonzero value effectively means <quote>it's an array</quote>.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attcacheoff</structfield> <type>int4</type>
      </para>
      <para>
       Always -1 in storage, but when loaded into a row descriptor
       in memory this might be updated to cache the offset of the attribute
       within the row
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>atttypmod</structfield> <type>int4</type>
      </para>
      <para>
       <structfield>atttypmod</structfield> records type-specific data
       supplied at table creation time (for example, the maximum
       length of a <type>varchar</type> column).  It is passed to
       type-specific input functions and length coercion functions.
       The value will generally be -1 for types that do not need <structfield>atttypmod</structfield>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attbyval</structfield> <type>bool</type>
      </para>
      <para>
       A copy of <literal>pg_type.typbyval</literal> of this column's type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attalign</structfield> <type>char</type>
      </para>
      <para>
       A copy of <literal>pg_type.typalign</literal> of this column's type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attstorage</structfield> <type>char</type>
      </para>
      <para>
       Normally a copy of <literal>pg_type.typstorage</literal> of this
       column's type.  For TOAST-able data types, this can be altered
       after column creation to control storage policy.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attcompression</structfield> <type>char</type>
      </para>
      <para>
       The current compression method of the column.  Typically this is
       <literal>'\0'</literal> to specify use of the current default setting
       (see <xref linkend="guc-default-toast-compression"/>).  Otherwise,
       <literal>'p'</literal> selects pglz compression, while
       <literal>'l'</literal> selects <productname>LZ4</productname>
       compression.  However, this field is ignored
       whenever <structfield>attstorage</structfield> does not allow
       compression.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attnotnull</structfield> <type>bool</type>
      </para>
      <para>
       This represents a not-null constraint.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>atthasdef</structfield> <type>bool</type>
      </para>
      <para>
       This column has a default expression or generation expression, in which
       case there will be a corresponding entry in the
       <link linkend="catalog-pg-attrdef"><structname>pg_attrdef</structname></link> catalog that actually defines the
       expression.  (Check <structfield>attgenerated</structfield> to
       determine whether this is a default or a generation expression.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>atthasmissing</structfield> <type>bool</type>
      </para>
      <para>
       This column has a value which is used where the column is entirely
       missing from the row, as happens when a column is added with a
       non-volatile <literal>DEFAULT</literal> value after the row is created.
       The actual value used is stored in the
       <structfield>attmissingval</structfield> column.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attidentity</structfield> <type>char</type>
      </para>
      <para>
       If a zero byte (<literal>''</literal>), then not an identity column.
       Otherwise, <literal>a</literal> = generated
       always, <literal>d</literal> = generated by default.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attgenerated</structfield> <type>char</type>
      </para>
      <para>
       If a zero byte (<literal>''</literal>), then not a generated column.
       Otherwise, <literal>s</literal> = stored.  (Other values might be added
       in the future.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attisdropped</structfield> <type>bool</type>
      </para>
      <para>
       This column has been dropped and is no longer valid.  A dropped
       column is still physically present in the table, but is
       ignored by the parser and so cannot be accessed via SQL.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attislocal</structfield> <type>bool</type>
      </para>
      <para>
       This column is defined locally in the relation.  Note that a column can
       be locally defined and inherited simultaneously.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attinhcount</structfield> <type>int4</type>
      </para>
      <para>
       The number of direct ancestors this column has.  A column with a
       nonzero number of ancestors cannot be dropped nor renamed.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attcollation</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The defined collation of the column, or zero if the column is
       not of a collatable data type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Column-level access privileges, if any have been granted specifically
       on this column
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attoptions</structfield> <type>text[]</type>
      </para>
      <para>
       Attribute-level options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attfdwoptions</structfield> <type>text[]</type>
      </para>
      <para>
       Attribute-level foreign data wrapper options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attmissingval</structfield> <type>anyarray</type>
      </para>
      <para>
       This column has a one element array containing the value used when the
       column is entirely missing from the row, as happens when the column is
       added with a non-volatile <literal>DEFAULT</literal> value after the
       row is created.  The value is only used when
       <structfield>atthasmissing</structfield> is true.  If there is no value
       the column is null.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   In a dropped column's <structname>pg_attribute</structname> entry,
   <structfield>atttypid</structfield> is reset to zero, but
   <structfield>attlen</structfield> and the other fields copied from
   <link linkend="catalog-pg-type"><structname>pg_type</structname></link> are still valid.  This arrangement is needed
   to cope with the situation where the dropped column's data type was
   later dropped, and so there is no <structname>pg_type</structname> row anymore.
   <structfield>attlen</structfield> and the other fields can be used
   to interpret the contents of a row of the table.
  </para>
 </sect1>


 <sect1 id="catalog-pg-authid">
  <title><structname>pg_authid</structname></title>

  <indexterm zone="catalog-pg-authid">
   <primary>pg_authid</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_authid</structname> contains information about
   database authorization identifiers (roles).  A role subsumes the concepts
   of <quote>users</quote> and <quote>groups</quote>.  A user is essentially just a
   role with the <structfield>rolcanlogin</structfield> flag set.  Any role (with or
   without <structfield>rolcanlogin</structfield>) can have other roles as members; see
   <link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link>.
  </para>

  <para>
   Since this catalog contains passwords, it must not be publicly readable.
   <link linkend="view-pg-roles"><structname>pg_roles</structname></link>
   is a publicly readable view on
   <structname>pg_authid</structname> that blanks out the password field.
  </para>

  <para>
   <xref linkend="user-manag"/> contains detailed information about user and
   privilege management.
  </para>

  <para>
   Because user identities are cluster-wide,
   <structname>pg_authid</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_authid</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_authid</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolname</structfield> <type>name</type>
      </para>
      <para>
       Role name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolsuper</structfield> <type>bool</type>
      </para>
      <para>
       Role has superuser privileges
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolinherit</structfield> <type>bool</type>
      </para>
      <para>
       Role automatically inherits privileges of roles it is a
       member of
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcreaterole</structfield> <type>bool</type>
      </para>
      <para>
       Role can create more roles
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcreatedb</structfield> <type>bool</type>
      </para>
      <para>
       Role can create databases
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcanlogin</structfield> <type>bool</type>
      </para>
      <para>
       Role can log in. That is, this role can be given as the initial
       session authorization identifier.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolreplication</structfield> <type>bool</type>
      </para>
      <para>
       Role is a replication role. A replication role can initiate replication
       connections and create and drop replication slots.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolbypassrls</structfield> <type>bool</type>
      </para>
      <para>
       Role bypasses every row-level security policy, see
       <xref linkend="ddl-rowsecurity"/> for more information.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolconnlimit</structfield> <type>int4</type>
      </para>
      <para>
       For roles that can log in, this sets maximum number of concurrent
       connections this role can make.  -1 means no limit.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolpassword</structfield> <type>text</type>
      </para>
      <para>
       Password (possibly encrypted); null if none. The format depends
       on the form of encryption used.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolvaliduntil</structfield> <type>timestamptz</type>
      </para>
      <para>
       Password expiry time (only used for password authentication);
       null if no expiration
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   For an MD5 encrypted password, <structfield>rolpassword</structfield>
   column will begin with the string <literal>md5</literal> followed by a
   32-character hexadecimal MD5 hash. The MD5 hash will be of the user's
   password concatenated to their user name. For example, if user
   <literal>joe</literal> has password <literal>xyzzy</literal>, <productname>PostgreSQL</productname>
   will store the md5 hash of <literal>xyzzyjoe</literal>.
  </para>

  <para>
   If the password is encrypted with SCRAM-SHA-256, it has the format:
<synopsis>
SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&lt;salt&gt;</replaceable>$<replaceable>&lt;StoredKey&gt;</replaceable>:<replaceable>&lt;ServerKey&gt;</replaceable>
</synopsis>
   where <replaceable>salt</replaceable>, <replaceable>StoredKey</replaceable> and
   <replaceable>ServerKey</replaceable> are in Base64 encoded format. This format is
   the same as that specified by <ulink url="https://tools.ietf.org/html/rfc5803">RFC 5803</ulink>.
  </para>

  <para>
    A password that does not follow either of those formats is assumed to be
    unencrypted.
  </para>
 </sect1>


 <sect1 id="catalog-pg-auth-members">
  <title><structname>pg_auth_members</structname></title>

  <indexterm zone="catalog-pg-auth-members">
   <primary>pg_auth_members</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_auth_members</structname> shows the membership
   relations between roles.  Any non-circular set of relationships is allowed.
  </para>

  <para>
   Because user identities are cluster-wide,
   <structname>pg_auth_members</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_auth_members</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_auth_members</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>roleid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       ID of a role that has a member
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>member</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       ID of a role that is a member of <structfield>roleid</structfield>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>grantor</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       ID of the role that granted this membership
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>admin_option</structfield> <type>bool</type>
      </para>
      <para>
       True if <structfield>member</structfield> can grant membership in
       <structfield>roleid</structfield> to others
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-cast">
  <title><structname>pg_cast</structname></title>

  <indexterm zone="catalog-pg-cast">
   <primary>pg_cast</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_cast</structname> stores data type conversion
   paths, both built-in and user-defined.
  </para>

  <para>
   It should be noted that <structname>pg_cast</structname> does not represent
   every type conversion that the system knows how to perform; only those that
   cannot be deduced from some generic rule.  For example, casting between a
   domain and its base type is not explicitly represented in
   <structname>pg_cast</structname>.  Another important exception is that
   <quote>automatic I/O conversion casts</quote>, those performed using a data
   type's own I/O functions to convert to or from <type>text</type> or other
   string types, are not explicitly represented in
   <structname>pg_cast</structname>.
  </para>

  <table>
   <title><structname>pg_cast</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>castsource</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the source data type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>casttarget</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the target data type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>castfunc</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the function to use to perform this cast.  Zero is
       stored if the cast method doesn't require a function.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>castcontext</structfield> <type>char</type>
      </para>
      <para>
       Indicates what contexts the cast can be invoked in.
       <literal>e</literal> means only as an explicit cast (using
       <literal>CAST</literal> or <literal>::</literal> syntax).
       <literal>a</literal> means implicitly in assignment
       to a target column, as well as explicitly.
       <literal>i</literal> means implicitly in expressions, as well as the
       other cases.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>castmethod</structfield> <type>char</type>
      </para>
      <para>
       Indicates how the cast is performed.
       <literal>f</literal> means that the function specified in the <structfield>castfunc</structfield> field is used.
       <literal>i</literal> means that the input/output functions are used.
       <literal>b</literal> means that the types are binary-coercible, thus no conversion is required.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The cast functions listed in <structname>pg_cast</structname> must
   always take the cast source type as their first argument type, and
   return the cast destination type as their result type.  A cast
   function can have up to three arguments.  The second argument,
   if present, must be type <type>integer</type>; it receives the type
   modifier associated with the destination type, or -1
   if there is none.  The third argument,
   if present, must be type <type>boolean</type>; it receives <literal>true</literal>
   if the cast is an explicit cast, <literal>false</literal> otherwise.
  </para>

  <para>
   It is legitimate to create a <structname>pg_cast</structname> entry
   in which the source and target types are the same, if the associated
   function takes more than one argument.  Such entries represent
   <quote>length coercion functions</quote> that coerce values of the type
   to be legal for a particular type modifier value.
  </para>

  <para>
   When a <structname>pg_cast</structname> entry has different source and
   target types and a function that takes more than one argument, it
   represents converting from one type to another and applying a length
   coercion in a single step.  When no such entry is available, coercion
   to a type that uses a type modifier involves two steps, one to
   convert between data types and a second to apply the modifier.
  </para>
 </sect1>

 <sect1 id="catalog-pg-class">
  <title><structname>pg_class</structname></title>

  <indexterm zone="catalog-pg-class">
   <primary>pg_class</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_class</structname> catalogs tables and most
   everything else that has columns or is otherwise similar to a
   table.  This includes indexes (but see also <link
   linkend="catalog-pg-index"><structname>pg_index</structname></link>),
   sequences (but see also <link
   linkend="catalog-pg-sequence"><structname>pg_sequence</structname></link>),
   views, materialized views, composite types, and TOAST tables;
   see <structfield>relkind</structfield>.
   Below, when we mean all of these kinds of objects we speak of
   <quote>relations</quote>.  Not all columns are meaningful for all relation
   types.
  </para>

  <table>
   <title><structname>pg_class</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relname</structfield> <type>name</type>
      </para>
      <para>
       Name of the table, index, view, etc.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reltype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the data type that corresponds to this table's row type,
       if any; zero for indexes, sequences, and toast tables, which have
       no <structname>pg_type</structname> entry
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reloftype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       For typed tables, the OID of the underlying composite type;
       zero for all other relations
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relam</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-am"><structname>pg_am</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If this is a table or an index, the access method used (heap,
       B-tree, hash, etc.); otherwise zero (zero occurs for sequences,
       as well as relations without storage, such as views)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relfilenode</structfield> <type>oid</type>
      </para>
      <para>
       Name of the on-disk file of this relation; zero means this
       is a <quote>mapped</quote> relation whose disk file name is determined
       by low-level state
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reltablespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The tablespace in which this relation is stored.  If zero,
       the database's default tablespace is implied.  (Not meaningful
       if the relation has no on-disk file.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relpages</structfield> <type>int4</type>
      </para>
      <para>
       Size of the on-disk representation of this table in pages (of size
       <symbol>BLCKSZ</symbol>).  This is only an estimate used by the
       planner.  It is updated by <link linkend="sql-vacuum"><command>VACUUM</command></link>,
       <link linkend="sql-analyze"><command>ANALYZE</command></link>, and a few DDL commands such as
       <link linkend="sql-createindex"><command>CREATE INDEX</command></link>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reltuples</structfield> <type>float4</type>
      </para>
      <para>
       Number of live rows in the table.  This is only an estimate used by
       the planner.  It is updated by <link linkend="sql-vacuum"><command>VACUUM</command></link>,
       <link linkend="sql-analyze"><command>ANALYZE</command></link>, and a few DDL commands such as
       <link linkend="sql-createindex"><command>CREATE INDEX</command></link>.
       If the table has never yet been vacuumed or
       analyzed, <structfield>reltuples</structfield>
       contains <literal>-1</literal> indicating that the row count is
       unknown.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relallvisible</structfield> <type>int4</type>
      </para>
      <para>
       Number of pages that are marked all-visible in the table's
       visibility map.  This is only an estimate used by the
       planner.  It is updated by <link linkend="sql-vacuum"><command>VACUUM</command></link>,
       <link linkend="sql-analyze"><command>ANALYZE</command></link>, and a few DDL commands such as
       <link linkend="sql-createindex"><command>CREATE INDEX</command></link>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reltoastrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the TOAST table associated with this table, zero if none.  The
       TOAST table stores large attributes <quote>out of line</quote> in a
       secondary table.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relhasindex</structfield> <type>bool</type>
      </para>
      <para>
       True if this is a table and it has (or recently had) any indexes
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relisshared</structfield> <type>bool</type>
      </para>
      <para>
       True if this table is shared across all databases in the cluster.  Only
       certain system catalogs (such as <link linkend="catalog-pg-database"><structname>pg_database</structname></link>)
       are shared.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relpersistence</structfield> <type>char</type>
      </para>
      <para>
       <literal>p</literal> = permanent table, <literal>u</literal> = unlogged table,
       <literal>t</literal> = temporary table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relkind</structfield> <type>char</type>
      </para>
      <para>
       <literal>r</literal> = ordinary table,
       <literal>i</literal> = index,
       <literal>S</literal> = sequence,
       <literal>t</literal> = TOAST table,
       <literal>v</literal> = view,
       <literal>m</literal> = materialized view,
       <literal>c</literal> = composite type,
       <literal>f</literal> = foreign table,
       <literal>p</literal> = partitioned table,
       <literal>I</literal> = partitioned index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relnatts</structfield> <type>int2</type>
      </para>
      <para>
       Number of user columns in the relation (system columns not
       counted).  There must be this many corresponding entries in
       <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.  See also
       <structname>pg_attribute</structname>.<structfield>attnum</structfield>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relchecks</structfield> <type>int2</type>
      </para>
      <para>
       Number of <literal>CHECK</literal> constraints on the table; see
       <link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link> catalog
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relhasrules</structfield> <type>bool</type>
      </para>
      <para>
       True if table has (or once had) rules; see
       <link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link> catalog
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relhastriggers</structfield> <type>bool</type>
      </para>
      <para>
       True if table has (or once had) triggers; see
       <link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link> catalog
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relhassubclass</structfield> <type>bool</type>
      </para>
      <para>
       True if table or index has (or once had) any inheritance children
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relrowsecurity</structfield> <type>bool</type>
      </para>
      <para>
       True if table has row-level security enabled; see
       <link linkend="catalog-pg-policy"><structname>pg_policy</structname></link> catalog
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relforcerowsecurity</structfield> <type>bool</type>
      </para>
      <para>
       True if row-level security (when enabled) will also apply to table owner; see
       <link linkend="catalog-pg-policy"><structname>pg_policy</structname></link> catalog
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relispopulated</structfield> <type>bool</type>
      </para>
      <para>
       True if relation is populated (this is true for all
       relations other than some materialized views)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relreplident</structfield> <type>char</type>
      </para>
      <para>
       Columns used to form <quote>replica identity</quote> for rows:
       <literal>d</literal> = default (primary key, if any),
       <literal>n</literal> = nothing,
       <literal>f</literal> = all columns,
       <literal>i</literal> = index with
       <structfield>indisreplident</structfield> set (same as nothing if the
       index used has been dropped)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relispartition</structfield> <type>bool</type>
      </para>
      <para>
       True if table or index is a partition
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relisivm</structfield> <type>bool</type>
      </para>
      <para>
       True if relation is incrementally maintainable materialized view
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relrewrite</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       For new relations being written during a DDL operation that requires a
       table rewrite, this contains the OID of the original relation;
       otherwise zero.  That state is only visible internally; this field should
       never contain anything other than zero for a user-visible relation.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relfrozenxid</structfield> <type>xid</type>
      </para>
      <para>
       All transaction IDs before this one have been replaced with a permanent
       (<quote>frozen</quote>) transaction ID in this table.  This is used to track
       whether the table needs to be vacuumed in order to prevent transaction
       ID wraparound or to allow <literal>pg_xact</literal> to be shrunk.  Zero
       (<symbol>InvalidTransactionId</symbol>) if the relation is not a table.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relminmxid</structfield> <type>xid</type>
      </para>
      <para>
       All multixact IDs before this one have been replaced by a
       transaction ID in this table.  This is used to track
       whether the table needs to be vacuumed in order to prevent multixact ID
       wraparound or to allow <literal>pg_multixact</literal> to be shrunk.  Zero
       (<symbol>InvalidMultiXactId</symbol>) if the relation is not a table.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reloptions</structfield> <type>text[]</type>
      </para>
      <para>
       Access-method-specific options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relpartbound</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       If table is a partition (see <structfield>relispartition</structfield>),
       internal representation of the partition bound
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Several of the Boolean flags in <structname>pg_class</structname> are maintained
   lazily: they are guaranteed to be true if that's the correct state, but
   may not be reset to false immediately when the condition is no longer
   true.  For example, <structfield>relhasindex</structfield> is set by
   <link linkend="sql-createindex"><command>CREATE INDEX</command></link>, but it is never cleared by
   <link linkend="sql-dropindex"><command>DROP INDEX</command></link>.  Instead, <link linkend="sql-vacuum"><command>VACUUM</command></link> clears
   <structfield>relhasindex</structfield> if it finds the table has no indexes.  This
   arrangement avoids race conditions and improves concurrency.
  </para>
 </sect1>

 <sect1 id="catalog-pg-collation">
  <title><structname>pg_collation</structname></title>

  <indexterm zone="catalog-pg-collation">
   <primary>pg_collation</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_collation</structname> describes the
   available collations, which are essentially mappings from an SQL
   name to operating system locale categories.
   See <xref linkend="collation"/> for more information.
  </para>

  <table>
   <title><structname>pg_collation</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collname</structfield> <type>name</type>
      </para>
      <para>
       Collation name (unique per namespace and encoding)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this collation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the collation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collprovider</structfield> <type>char</type>
      </para>
      <para>
       Provider of the collation: <literal>d</literal> = database
       default, <literal>c</literal> = libc, <literal>i</literal> = icu
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collisdeterministic</structfield> <type>bool</type>
      </para>
      <para>
       Is the collation deterministic?
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collencoding</structfield> <type>int4</type>
      </para>
      <para>
       Encoding in which the collation is applicable, or -1 if it
       works for any encoding
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collcollate</structfield> <type>name</type>
      </para>
      <para>
       <symbol>LC_COLLATE</symbol> for this collation object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collctype</structfield> <type>name</type>
      </para>
      <para>
       <symbol>LC_CTYPE</symbol> for this collation object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>collversion</structfield> <type>text</type>
      </para>
      <para>
       Provider-specific version of the collation.  This is recorded when the
       collation is created and then checked when it is used, to detect
       changes in the collation definition that could lead to data corruption.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Note that the unique key on this catalog is (<structfield>collname</structfield>,
   <structfield>collencoding</structfield>, <structfield>collnamespace</structfield>) not just
   (<structfield>collname</structfield>, <structfield>collnamespace</structfield>).
   <productname>PostgreSQL</productname> generally ignores all
   collations that do not have <structfield>collencoding</structfield> equal to
   either the current database's encoding or -1, and creation of new entries
   with the same name as an entry with <structfield>collencoding</structfield> = -1
   is forbidden.  Therefore it is sufficient to use a qualified SQL name
   (<replaceable>schema</replaceable>.<replaceable>name</replaceable>) to identify a collation,
   even though this is not unique according to the catalog definition.
   The reason for defining the catalog this way is that
   <application>initdb</application> fills it in at cluster initialization time with
   entries for all locales available on the system, so it must be able to
   hold entries for all encodings that might ever be used in the cluster.
  </para>

  <para>
   In the <literal>template0</literal> database, it could be useful to create
   collations whose encoding does not match the database encoding,
   since they could match the encodings of databases later cloned from
   <literal>template0</literal>.  This would currently have to be done manually.
  </para>
 </sect1>

 <sect1 id="catalog-pg-constraint">
  <title><structname>pg_constraint</structname></title>

  <indexterm zone="catalog-pg-constraint">
   <primary>pg_constraint</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_constraint</structname> stores check, primary
   key, unique, foreign key, and exclusion constraints on tables.
   (Column constraints are not treated specially.  Every column constraint is
   equivalent to some table constraint.)
   Not-null constraints are represented in the
   <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>
   catalog, not here.
  </para>

  <para>
   User-defined constraint triggers (created with <link linkend="sql-createtrigger">
   <command>CREATE CONSTRAINT TRIGGER</command></link>) also give rise to an entry in this table.
  </para>

  <para>
   Check constraints on domains are stored here, too.
  </para>

  <table>
   <title><structname>pg_constraint</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conname</structfield> <type>name</type>
      </para>
      <para>
       Constraint name (not necessarily unique!)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>connamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this constraint
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>contype</structfield> <type>char</type>
      </para>
      <para>
       <literal>c</literal> = check constraint,
       <literal>f</literal> = foreign key constraint,
       <literal>p</literal> = primary key constraint,
       <literal>u</literal> = unique constraint,
       <literal>t</literal> = constraint trigger,
       <literal>x</literal> = exclusion constraint
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>condeferrable</structfield> <type>bool</type>
      </para>
      <para>
       Is the constraint deferrable?
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>condeferred</structfield> <type>bool</type>
      </para>
      <para>
       Is the constraint deferred by default?
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>convalidated</structfield> <type>bool</type>
      </para>
      <para>
       Has the constraint been validated?
       Currently, can be false only for foreign keys and CHECK constraints
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The table this constraint is on; zero if not a table constraint
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>contypid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The domain this constraint is on; zero if not a domain constraint
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conindid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The index supporting this constraint, if it's a unique, primary
       key, foreign key, or exclusion constraint; else zero
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conparentid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The corresponding constraint of the parent partitioned table,
       if this is a constraint on a partition; else zero
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If a foreign key, the referenced table; else zero
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confupdtype</structfield> <type>char</type>
      </para>
      <para>
       Foreign key update action code:
       <literal>a</literal> = no action,
       <literal>r</literal> = restrict,
       <literal>c</literal> = cascade,
       <literal>n</literal> = set null,
       <literal>d</literal> = set default
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confdeltype</structfield> <type>char</type>
      </para>
      <para>
       Foreign key deletion action code:
       <literal>a</literal> = no action,
       <literal>r</literal> = restrict,
       <literal>c</literal> = cascade,
       <literal>n</literal> = set null,
       <literal>d</literal> = set default
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confmatchtype</structfield> <type>char</type>
      </para>
      <para>
       Foreign key match type:
       <literal>f</literal> = full,
       <literal>p</literal> = partial,
       <literal>s</literal> = simple
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conislocal</structfield> <type>bool</type>
      </para>
      <para>
       This constraint is defined locally for the relation.  Note that a
       constraint can be locally defined and inherited simultaneously.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>coninhcount</structfield> <type>int4</type>
      </para>
      <para>
       The number of direct inheritance ancestors this constraint has.
       A constraint with
       a nonzero number of ancestors cannot be dropped nor renamed.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>connoinherit</structfield> <type>bool</type>
      </para>
      <para>
       This constraint is defined locally for the relation.  It is a
       non-inheritable constraint.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conkey</structfield> <type>int2[]</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attnum</structfield>)
      </para>
      <para>
       If a table constraint (including foreign keys, but not constraint
       triggers), list of the constrained columns
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confkey</structfield> <type>int2[]</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attnum</structfield>)
      </para>
      <para>
       If a foreign key, list of the referenced columns
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conpfeqop</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If a foreign key, list of the equality operators for PK = FK comparisons
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conppeqop</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If a foreign key, list of the equality operators for PK = PK comparisons
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conffeqop</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If a foreign key, list of the equality operators for FK = FK comparisons
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conexclop</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If an exclusion constraint, list of the per-column exclusion operators
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conbin</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       If a check constraint, an internal representation of the
       expression.  (It's recommended to use
       <function>pg_get_constraintdef()</function> to extract the definition of
       a check constraint.)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   In the case of an exclusion constraint, <structfield>conkey</structfield>
   is only useful for constraint elements that are simple column references.
   For other cases, a zero appears in <structfield>conkey</structfield>
   and the associated index must be consulted to discover the expression
   that is constrained.  (<structfield>conkey</structfield> thus has the
   same contents as <link linkend="catalog-pg-index"><structname>pg_index</structname></link>.<structfield>indkey</structfield> for the
   index.)
  </para>

  <note>
   <para>
    <literal>pg_class.relchecks</literal> needs to agree with the
    number of check-constraint entries found in this table for each
    relation.
   </para>
  </note>
 </sect1>


 <sect1 id="catalog-pg-conversion">
  <title><structname>pg_conversion</structname></title>

  <indexterm zone="catalog-pg-conversion">
   <primary>pg_conversion</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_conversion</structname> describes
   encoding conversion functions.  See <xref linkend="sql-createconversion"/>
   for more information.
  </para>

  <table>
   <title><structname>pg_conversion</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conname</structfield> <type>name</type>
      </para>
      <para>
       Conversion name (unique within a namespace)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>connamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this conversion
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the conversion
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conforencoding</structfield> <type>int4</type>
      </para>
      <para>
       Source encoding ID
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>contoencoding</structfield> <type>int4</type>
      </para>
      <para>
       Destination encoding ID
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conproc</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Conversion function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>condefault</structfield> <type>bool</type>
      </para>
      <para>
       True if this is the default conversion
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="catalog-pg-database">
  <title><structname>pg_database</structname></title>

  <indexterm zone="catalog-pg-database">
   <primary>pg_database</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_database</structname> stores information about
   the available databases.  Databases are created with the <link
   linkend="sql-createdatabase"><command>CREATE DATABASE</command></link> command.
   Consult <xref linkend="managing-databases"/> for details about the meaning
   of some of the parameters.
  </para>

  <para>
   Unlike most system catalogs, <structname>pg_database</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_database</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_database</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Database name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datdba</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the database, usually the user who created it
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>encoding</structfield> <type>int4</type>
      </para>
      <para>
       Character encoding for this database
       (<function>pg_encoding_to_char()</function> can translate
       this number to the encoding name)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datcollate</structfield> <type>name</type>
      </para>
      <para>
       LC_COLLATE for this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datctype</structfield> <type>name</type>
      </para>
      <para>
       LC_CTYPE for this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datistemplate</structfield> <type>bool</type>
      </para>
      <para>
       If true, then this database can be cloned by
       any user with <literal>CREATEDB</literal> privileges;
       if false, then only superusers or the owner of
       the database can clone it.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datallowconn</structfield> <type>bool</type>
      </para>
      <para>
       If false then no one can connect to this database.  This is
       used to protect the <literal>template0</literal> database from being altered.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datconnlimit</structfield> <type>int4</type>
      </para>
      <para>
       Sets maximum number of concurrent connections that can be made
       to this database.  -1 means no limit.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datlastsysoid</structfield> <type>oid</type>
      </para>
      <para>
       Last system OID in the database; useful
       particularly to <application>pg_dump</application>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datfrozenxid</structfield> <type>xid</type>
      </para>
      <para>
       All transaction IDs before this one have been replaced with a permanent
       (<quote>frozen</quote>) transaction ID in this database.  This is used to
       track whether the database needs to be vacuumed in order to prevent
       transaction ID wraparound or to allow <literal>pg_xact</literal> to be shrunk.
       It is the minimum of the per-table
       <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relfrozenxid</structfield> values.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datminmxid</structfield> <type>xid</type>
      </para>
      <para>
       All multixact IDs before this one have been replaced with a
       transaction ID in this database.  This is used to
       track whether the database needs to be vacuumed in order to prevent
       multixact ID wraparound or to allow <literal>pg_multixact</literal> to be shrunk.
       It is the minimum of the per-table
       <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relminmxid</structfield> values.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dattablespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The default tablespace for the database.
       Within this database, all tables for which
       <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>reltablespace</structfield> is zero
       will be stored in this tablespace; in particular, all the non-shared
       system catalogs will be there.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-db-role-setting">
  <title><structname>pg_db_role_setting</structname></title>

  <indexterm zone="catalog-pg-db-role-setting">
   <primary>pg_db_role_setting</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_db_role_setting</structname> records the default
   values that have been set for run-time configuration variables,
   for each role and database combination.
  </para>

  <para>
   Unlike most system catalogs, <structname>pg_db_role_setting</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_db_role_setting</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_db_role_setting</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>setdatabase</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-database"><structname>pg_database</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the database the setting is applicable to, or zero if not database-specific
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>setrole</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the role the setting is applicable to, or zero if not role-specific
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>setconfig</structfield> <type>text[]</type>
      </para>
      <para>
       Defaults for run-time configuration variables
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-default-acl">
  <title><structname>pg_default_acl</structname></title>

  <indexterm zone="catalog-pg-default-acl">
   <primary>pg_default_acl</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_default_acl</structname> stores initial
   privileges to be assigned to newly created objects.
  </para>

  <table>
   <title><structname>pg_default_acl</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>defaclrole</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the role associated with this entry
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>defaclnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace associated with this entry,
       or zero if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>defaclobjtype</structfield> <type>char</type>
      </para>
      <para>
       Type of object this entry is for:
       <literal>r</literal> = relation (table, view),
       <literal>S</literal> = sequence,
       <literal>f</literal> = function,
       <literal>T</literal> = type,
       <literal>n</literal> = schema
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>defaclacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges that this type of object should have on creation
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   A <structname>pg_default_acl</structname> entry shows the initial privileges to
   be assigned to an object belonging to the indicated user.  There are
   currently two types of entry: <quote>global</quote> entries with
   <structfield>defaclnamespace</structfield> = zero, and <quote>per-schema</quote> entries
   that reference a particular schema.  If a global entry is present then
   it <emphasis>overrides</emphasis> the normal hard-wired default privileges
   for the object type.  A per-schema entry, if present, represents privileges
   to be <emphasis>added to</emphasis> the global or hard-wired default privileges.
  </para>

  <para>
   Note that when an ACL entry in another catalog is null, it is taken
   to represent the hard-wired default privileges for its object,
   <emphasis>not</emphasis> whatever might be in <structname>pg_default_acl</structname>
   at the moment.  <structname>pg_default_acl</structname> is only consulted during
   object creation.
  </para>

 </sect1>


 <sect1 id="catalog-pg-depend">
  <title><structname>pg_depend</structname></title>

  <indexterm zone="catalog-pg-depend">
   <primary>pg_depend</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_depend</structname> records the dependency
   relationships between database objects.  This information allows
   <command>DROP</command> commands to find which other objects must be dropped
   by <command>DROP CASCADE</command> or prevent dropping in the <command>DROP
   RESTRICT</command> case.
  </para>

  <para>
   See also <link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link>,
   which performs a similar function for dependencies involving objects
   that are shared across a database cluster.
  </para>

  <table>
   <title><structname>pg_depend</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog the dependent object is in,
       or zero for a <symbol>DEPENDENCY_PIN</symbol> entry
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the specific dependent object,
       or zero for a <symbol>DEPENDENCY_PIN</symbol> entry
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objsubid</structfield> <type>int4</type>
      </para>
      <para>
       For a table column, this is the column number (the
       <structfield>objid</structfield> and <structfield>classid</structfield> refer to the
       table itself).  For all other object types, this column is
       zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>refclassid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog the referenced object is in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>refobjid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the specific referenced object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>refobjsubid</structfield> <type>int4</type>
      </para>
      <para>
       For a table column, this is the column number (the
       <structfield>refobjid</structfield> and <structfield>refclassid</structfield> refer
       to the table itself).  For all other object types, this column
       is zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>deptype</structfield> <type>char</type>
      </para>
      <para>
       A code defining the specific semantics of this dependency relationship; see text
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   In all cases, a <structname>pg_depend</structname> entry indicates that the
   referenced object cannot be dropped without also dropping the dependent
   object.  However, there are several subflavors identified by
   <structfield>deptype</structfield>:

   <variablelist>
    <varlistentry>
     <term><symbol>DEPENDENCY_NORMAL</symbol> (<literal>n</literal>)</term>
     <listitem>
      <para>
       A normal relationship between separately-created objects.  The
       dependent object can be dropped without affecting the
       referenced object.  The referenced object can only be dropped
       by specifying <literal>CASCADE</literal>, in which case the dependent
       object is dropped, too.  Example: a table column has a normal
       dependency on its data type.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>DEPENDENCY_AUTO</symbol> (<literal>a</literal>)</term>
     <listitem>
      <para>
       The dependent object can be dropped separately from the
       referenced object, and should be automatically dropped
       (regardless of <literal>RESTRICT</literal> or <literal>CASCADE</literal>
       mode) if the referenced object is dropped.  Example: a named
       constraint on a table is made auto-dependent on the table, so
       that it will go away if the table is dropped.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>DEPENDENCY_INTERNAL</symbol> (<literal>i</literal>)</term>
     <listitem>
      <para>
       The dependent object was created as part of creation of the
       referenced object, and is really just a part of its internal
       implementation.  A direct <command>DROP</command> of the dependent
       object will be disallowed outright (we'll tell the user to issue
       a <command>DROP</command> against the referenced object, instead).
       A <command>DROP</command> of the referenced object will result in
       automatically dropping the dependent object
       whether <literal>CASCADE</literal> is specified or not.  If the
       dependent object has to be dropped due to a dependency on some other
       object being removed, its drop is converted to a drop of the referenced
       object, so that <literal>NORMAL</literal> and <literal>AUTO</literal>
       dependencies of the dependent object behave much like they were
       dependencies of the referenced object.
       Example: a view's <literal>ON SELECT</literal> rule is made
       internally dependent on the view, preventing it from being dropped
       while the view remains.  Dependencies of the rule (such as tables it
       refers to) act as if they were dependencies of the view.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>DEPENDENCY_PARTITION_PRI</symbol> (<literal>P</literal>)</term>
     <term><symbol>DEPENDENCY_PARTITION_SEC</symbol> (<literal>S</literal>)</term>
     <listitem>
      <para>
       The dependent object was created as part of creation of the
       referenced object, and is really just a part of its internal
       implementation; however, unlike <literal>INTERNAL</literal>,
       there is more than one such referenced object.  The dependent object
       must not be dropped unless at least one of these referenced objects
       is dropped; if any one is, the dependent object should be dropped
       whether or not <literal>CASCADE</literal> is specified.  Also
       unlike <literal>INTERNAL</literal>, a drop of some other object
       that the dependent object depends on does not result in automatic
       deletion of any partition-referenced object.  Hence, if the drop
       does not cascade to at least one of these objects via some other
       path, it will be refused.  (In most cases, the dependent object
       shares all its non-partition dependencies with at least one
       partition-referenced object, so that this restriction does not
       result in blocking any cascaded delete.)
       Primary and secondary partition dependencies behave identically
       except that the primary dependency is preferred for use in error
       messages; hence, a partition-dependent object should have one
       primary partition dependency and one or more secondary partition
       dependencies.
       Note that partition dependencies are made in addition to, not
       instead of, any dependencies the object would normally have.  This
       simplifies <command>ATTACH/DETACH PARTITION</command> operations:
       the partition dependencies need only be added or removed.
       Example: a child partitioned index is made partition-dependent
       on both the partition table it is on and the parent partitioned
       index, so that it goes away if either of those is dropped, but
       not otherwise.  The dependency on the parent index is primary,
       so that if the user tries to drop the child partitioned index,
       the error message will suggest dropping the parent index instead
       (not the table).
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>DEPENDENCY_EXTENSION</symbol> (<literal>e</literal>)</term>
     <listitem>
      <para>
       The dependent object is a member of the <firstterm>extension</firstterm> that is
       the referenced object (see
       <link linkend="catalog-pg-extension"><structname>pg_extension</structname></link>).
       The dependent object can be dropped only via
       <link linkend="sql-dropextension"><command>DROP EXTENSION</command></link> on the referenced object.
       Functionally this dependency type acts the same as
       an <literal>INTERNAL</literal> dependency, but it's kept separate for
       clarity and to simplify <application>pg_dump</application>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>DEPENDENCY_AUTO_EXTENSION</symbol> (<literal>x</literal>)</term>
     <listitem>
      <para>
       The dependent object is not a member of the extension that is the
       referenced object (and so it should not be ignored
       by <application>pg_dump</application>), but it cannot function
       without the extension and should be auto-dropped if the extension is.
       The dependent object may be dropped on its own as well.
       Functionally this dependency type acts the same as
       an <literal>AUTO</literal> dependency, but it's kept separate for
       clarity and to simplify <application>pg_dump</application>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>DEPENDENCY_PIN</symbol> (<literal>p</literal>)</term>
     <listitem>
      <para>
       There is no dependent object; this type of entry is a signal
       that the system itself depends on the referenced object, and so
       that object must never be deleted.  Entries of this type are
       created only by <application>initdb</application>.  The columns for the
       dependent object contain zeroes.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>

   Other dependency flavors might be needed in future.
  </para>

  <para>
   Note that it's quite possible for two objects to be linked by more than
   one <structname>pg_depend</structname> entry.  For example, a child
   partitioned index would have both a partition-type dependency on its
   associated partition table, and an auto dependency on each column of
   that table that it indexes.  This sort of situation expresses the union
   of multiple dependency semantics.  A dependent object can be dropped
   without <literal>CASCADE</literal> if any of its dependencies satisfies
   its condition for automatic dropping.  Conversely, all the
   dependencies' restrictions about which objects must be dropped together
   must be satisfied.
  </para>

 </sect1>


 <sect1 id="catalog-pg-description">
  <title><structname>pg_description</structname></title>

  <indexterm zone="catalog-pg-description">
   <primary>pg_description</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_description</structname> stores optional descriptions
   (comments) for each database object.  Descriptions can be manipulated
   with the <link linkend="sql-comment"><command>COMMENT</command></link> command and viewed with
   <application>psql</application>'s <literal>\d</literal> commands.
   Descriptions of many built-in system objects are provided in the initial
   contents of <structname>pg_description</structname>.
  </para>

  <para>
   See also <link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link>,
   which performs a similar function for descriptions involving objects that
   are shared across a database cluster.
  </para>

  <table>
   <title><structname>pg_description</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objoid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the object this description pertains to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog this object appears in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objsubid</structfield> <type>int4</type>
      </para>
      <para>
       For a comment on a table column, this is the column number (the
       <structfield>objoid</structfield> and <structfield>classoid</structfield> refer to
       the table itself).  For all other object types, this column is
       zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>description</structfield> <type>text</type>
      </para>
      <para>
       Arbitrary text that serves as the description of this object
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-enum">
  <title><structname>pg_enum</structname></title>

  <indexterm zone="catalog-pg-enum">
   <primary>pg_enum</primary>
  </indexterm>

  <para>
   The <structname>pg_enum</structname> catalog contains entries
   showing the values and labels for each enum type. The
   internal representation of a given enum value is actually the OID
   of its associated row in <structname>pg_enum</structname>.
  </para>

  <table>
   <title><structname>pg_enum</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>enumtypid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the <link linkend="catalog-pg-type"><structname>pg_type</structname></link> entry owning this enum value
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>enumsortorder</structfield> <type>float4</type>
      </para>
      <para>
       The sort position of this enum value within its enum type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>enumlabel</structfield> <type>name</type>
      </para>
      <para>
       The textual label for this enum value
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The OIDs for <structname>pg_enum</structname> rows follow a special
   rule: even-numbered OIDs are guaranteed to be ordered in the same way
   as the sort ordering of their enum type.  That is, if two even OIDs
   belong to the same enum type, the smaller OID must have the smaller
   <structfield>enumsortorder</structfield> value.  Odd-numbered OID values
   need bear no relationship to the sort order.  This rule allows the
   enum comparison routines to avoid catalog lookups in many common cases.
   The routines that create and alter enum types attempt to assign even
   OIDs to enum values whenever possible.
  </para>

  <para>
   When an enum type is created, its members are assigned sort-order
   positions 1..<replaceable>n</replaceable>.  But members added later might be given
   negative or fractional values of <structfield>enumsortorder</structfield>.
   The only requirement on these values is that they be correctly
   ordered and unique within each enum type.
  </para>
 </sect1>


 <sect1 id="catalog-pg-event-trigger">
  <title><structname>pg_event_trigger</structname></title>

  <indexterm zone="catalog-pg-event-trigger">
   <primary>pg_event_trigger</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_event_trigger</structname> stores event triggers.
   See <xref linkend="event-triggers"/> for more information.
  </para>

  <table>
   <title><structname>pg_event_trigger</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>evtname</structfield> <type>name</type>
      </para>
      <para>
       Trigger name (must be unique)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>evtevent</structfield> <type>name</type>
      </para>
      <para>
       Identifies the event for which this trigger fires
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>evtowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the event trigger
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>evtfoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The function to be called
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>evtenabled</structfield> <type>char</type>
      </para>
      <para>
       Controls in which <xref linkend="guc-session-replication-role"/> modes
       the event trigger fires.
       <literal>O</literal> = trigger fires in <quote>origin</quote> and <quote>local</quote> modes,
       <literal>D</literal> = trigger is disabled,
       <literal>R</literal> = trigger fires in <quote>replica</quote> mode,
       <literal>A</literal> = trigger fires always.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>evttags</structfield> <type>text[]</type>
      </para>
      <para>
       Command tags for which this trigger will fire.  If NULL, the firing
       of this trigger is not restricted on the basis of the command tag.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-extension">
  <title><structname>pg_extension</structname></title>

  <indexterm zone="catalog-pg-extension">
   <primary>pg_extension</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_extension</structname> stores information
   about the installed extensions.  See <xref linkend="extend-extensions"/>
   for details about extensions.
  </para>

  <table>
   <title><structname>pg_extension</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extname</structfield> <type>name</type>
      </para>
      <para>
       Name of the extension
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the extension
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Schema containing the extension's exported objects
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extrelocatable</structfield> <type>bool</type>
      </para>
      <para>
       True if extension can be relocated to another schema
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extversion</structfield> <type>text</type>
      </para>
      <para>
       Version name for the extension
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extconfig</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Array of <type>regclass</type> OIDs for the extension's configuration
       table(s), or <literal>NULL</literal> if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extcondition</structfield> <type>text[]</type>
      </para>
      <para>
       Array of <literal>WHERE</literal>-clause filter conditions for the
       extension's configuration table(s), or <literal>NULL</literal> if none
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Note that unlike most catalogs with a <quote>namespace</quote> column,
   <structfield>extnamespace</structfield> is not meant to imply
   that the extension belongs to that schema.  Extension names are never
   schema-qualified.  Rather, <structfield>extnamespace</structfield>
   indicates the schema that contains most or all of the extension's
   objects.  If <structfield>extrelocatable</structfield> is true, then
   this schema must in fact contain all schema-qualifiable objects
   belonging to the extension.
  </para>
 </sect1>


 <sect1 id="catalog-pg-foreign-data-wrapper">
  <title><structname>pg_foreign_data_wrapper</structname></title>

  <indexterm zone="catalog-pg-foreign-data-wrapper">
   <primary>pg_foreign_data_wrapper</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_foreign_data_wrapper</structname> stores
   foreign-data wrapper definitions.  A foreign-data wrapper is the
   mechanism by which external data, residing on foreign servers, is
   accessed.
  </para>

  <table>
   <title><structname>pg_foreign_data_wrapper</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwname</structfield> <type>name</type>
      </para>
      <para>
       Name of the foreign-data wrapper
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the foreign-data wrapper
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwhandler</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       References a handler function that is responsible for
       supplying execution routines for the foreign-data wrapper.
       Zero if no handler is provided
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwvalidator</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       References a validator function that is responsible for
       checking the validity of the options given to the
       foreign-data wrapper, as well as options for foreign servers and user
       mappings using the foreign-data wrapper.  Zero if no validator
       is provided
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwoptions</structfield> <type>text[]</type>
      </para>
      <para>
       Foreign-data wrapper specific options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-foreign-server">
  <title><structname>pg_foreign_server</structname></title>

  <indexterm zone="catalog-pg-foreign-server">
   <primary>pg_foreign_server</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_foreign_server</structname> stores
   foreign server definitions.  A foreign server describes a source
   of external data, such as a remote server.  Foreign
   servers are accessed via foreign-data wrappers.
  </para>

  <table>
   <title><structname>pg_foreign_server</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvname</structfield> <type>name</type>
      </para>
      <para>
       Name of the foreign server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the foreign server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvfdw</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-foreign-data-wrapper"><structname>pg_foreign_data_wrapper</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the foreign-data wrapper of this foreign server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvtype</structfield> <type>text</type>
      </para>
      <para>
       Type of the server (optional)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvversion</structfield> <type>text</type>
      </para>
      <para>
       Version of the server (optional)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvoptions</structfield> <type>text[]</type>
      </para>
      <para>
       Foreign server specific options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-foreign-table">
  <title><structname>pg_foreign_table</structname></title>

  <indexterm zone="catalog-pg-foreign-table">
   <primary>pg_foreign_table</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_foreign_table</structname> contains
   auxiliary information about foreign tables.  A foreign table is
   primarily represented by a
   <link linkend="catalog-pg-class"><structname>pg_class</structname></link>
   entry, just like a regular table.  Its <structname>pg_foreign_table</structname>
   entry contains the information that is pertinent only to foreign tables
   and not any other kind of relation.
  </para>

  <table>
   <title><structname>pg_foreign_table</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ftrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the <link linkend="catalog-pg-class"><structname>pg_class</structname></link> entry for this foreign table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ftserver</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-foreign-server"><structname>pg_foreign_server</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the foreign server for this foreign table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ftoptions</structfield> <type>text[]</type>
      </para>
      <para>
       Foreign table options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-index">
  <title><structname>pg_index</structname></title>

  <indexterm zone="catalog-pg-index">
   <primary>pg_index</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_index</structname> contains part of the information
   about indexes.  The rest is mostly in
   <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.
  </para>

  <table>
   <title><structname>pg_index</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indexrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the <link linkend="catalog-pg-class"><structname>pg_class</structname></link> entry for this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the <link linkend="catalog-pg-class"><structname>pg_class</structname></link> entry for the table this index is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indnatts</structfield> <type>int2</type>
      </para>
      <para>
       The total number of columns in the index (duplicates
       <literal>pg_class.relnatts</literal>); this number includes both key and included attributes
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indnkeyatts</structfield> <type>int2</type>
      </para>
      <para>
       The number of <firstterm>key columns</firstterm> in the index,
       not counting any <firstterm>included columns</firstterm>, which are
       merely stored and do not participate in the index semantics
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indisunique</structfield> <type>bool</type>
      </para>
      <para>
       If true, this is a unique index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indisprimary</structfield> <type>bool</type>
      </para>
      <para>
       If true, this index represents the primary key of the table
       (<structfield>indisunique</structfield> should always be true when this is true)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indisexclusion</structfield> <type>bool</type>
      </para>
      <para>
       If true, this index supports an exclusion constraint
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indimmediate</structfield> <type>bool</type>
      </para>
      <para>
       If true, the uniqueness check is enforced immediately on
       insertion
       (irrelevant if <structfield>indisunique</structfield> is not true)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indisclustered</structfield> <type>bool</type>
      </para>
      <para>
       If true, the table was last clustered on this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indisvalid</structfield> <type>bool</type>
      </para>
      <para>
       If true, the index is currently valid for queries.  False means the
       index is possibly incomplete: it must still be modified by
       <link linkend="sql-insert"><command>INSERT</command></link>/<link linkend="sql-update"><command>UPDATE</command></link> operations, but it cannot safely
       be used for queries. If it is unique, the uniqueness property is not
       guaranteed true either.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indcheckxmin</structfield> <type>bool</type>
      </para>
      <para>
       If true, queries must not use the index until the <structfield>xmin</structfield>
       of this <structname>pg_index</structname> row is below their <symbol>TransactionXmin</symbol>
       event horizon, because the table may contain broken HOT chains with
       incompatible rows that they can see
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indisready</structfield> <type>bool</type>
      </para>
      <para>
       If true, the index is currently ready for inserts.  False means the
       index must be ignored by <link linkend="sql-insert"><command>INSERT</command></link>/<link linkend="sql-update"><command>UPDATE</command></link>
       operations.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indislive</structfield> <type>bool</type>
      </para>
      <para>
       If false, the index is in process of being dropped, and should be
       ignored for all purposes (including HOT-safety decisions)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indisreplident</structfield> <type>bool</type>
      </para>
      <para>
       If true this index has been chosen as <quote>replica identity</quote>
       using <link linkend="sql-altertable-replica-identity"><command>ALTER TABLE ...
       REPLICA IDENTITY USING INDEX ...</command></link>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indkey</structfield> <type>int2vector</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attnum</structfield>)
      </para>
      <para>
       This is an array of <structfield>indnatts</structfield> values that
       indicate which table columns this index indexes.  For example a value
       of <literal>1 3</literal> would mean that the first and the third table
       columns make up the index entries.  Key columns come before non-key
       (included) columns.  A zero in this array indicates that the
       corresponding index attribute is an expression over the table columns,
       rather than a simple column reference.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indcollation</structfield> <type>oidvector</type>
       (references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       For each column in the index key
       (<structfield>indnkeyatts</structfield> values), this contains the OID
       of the collation to use for the index, or zero if the column is not of
       a collatable data type.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indclass</structfield> <type>oidvector</type>
       (references <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       For each column in the index key
       (<structfield>indnkeyatts</structfield> values), this contains the OID
       of the operator class to use.  See
       <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link> for details.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indoption</structfield> <type>int2vector</type>
      </para>
      <para>
       This is an array of <structfield>indnkeyatts</structfield> values that
       store per-column flag bits.  The meaning of the bits is defined by
       the index's access method.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indexprs</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Expression trees (in <function>nodeToString()</function>
       representation) for index attributes that are not simple column
       references.  This is a list with one element for each zero
       entry in <structfield>indkey</structfield>.  Null if all index attributes
       are simple references.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indpred</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Expression tree (in <function>nodeToString()</function>
       representation) for partial index predicate.  Null if not a
       partial index.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-inherits">
  <title><structname>pg_inherits</structname></title>

  <indexterm zone="catalog-pg-inherits">
   <primary>pg_inherits</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_inherits</structname> records information about
   table and index inheritance hierarchies.  There is one entry for each direct
   parent-child table or index relationship in the database.  (Indirect
   inheritance can be determined by following chains of entries.)
  </para>

  <table>
   <title><structname>pg_inherits</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>inhrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the child table or index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>inhparent</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the parent table or index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>inhseqno</structfield> <type>int4</type>
      </para>
      <para>
       If there is more than one direct parent for a child table (multiple
       inheritance), this number tells the order in which the
       inherited columns are to be arranged.  The count starts at 1.
      </para>
      <para>
       Indexes cannot have multiple inheritance, since they can only inherit
       when using declarative partitioning.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>inhdetachpending</structfield> <type>bool</type>
      </para>
      <para>
       <literal>true</literal> for a partition that is in the process of
       being detached; <literal>false</literal> otherwise.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="catalog-pg-init-privs">
  <title><structname>pg_init_privs</structname></title>

  <indexterm zone="catalog-pg-init-privs">
   <primary>pg_init_privs</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_init_privs</structname> records information about
   the initial privileges of objects in the system.  There is one entry
   for each object in the database which has a non-default (non-NULL)
   initial set of privileges.
  </para>

  <para>
   Objects can have initial privileges either by having those privileges set
   when the system is initialized (by <application>initdb</application>) or when the
   object is created during a <link linkend="sql-createextension"><command>CREATE EXTENSION</command></link> and the
   extension script sets initial privileges using the <link linkend="sql-grant"><command>GRANT</command></link>
   system.  Note that the system will automatically handle recording of the
   privileges during the extension script and that extension authors need
   only use the <command>GRANT</command> and <command>REVOKE</command>
   statements in their script to have the privileges recorded.  The
   <literal>privtype</literal> column indicates if the initial privilege was
   set by <application>initdb</application> or during a
   <command>CREATE EXTENSION</command> command.
  </para>

  <para>
   Objects which have initial privileges set by <application>initdb</application> will
   have entries where <literal>privtype</literal> is
   <literal>'i'</literal>, while objects which have initial privileges set
   by <command>CREATE EXTENSION</command> will have entries where
   <literal>privtype</literal> is <literal>'e'</literal>.
  </para>

  <table>
   <title><structname>pg_init_privs</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objoid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the specific object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog the object is in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objsubid</structfield> <type>int4</type>
      </para>
      <para>
       For a table column, this is the column number (the
       <structfield>objoid</structfield> and <structfield>classoid</structfield> refer to the
       table itself).  For all other object types, this column is
       zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>privtype</structfield> <type>char</type>
      </para>
      <para>
       A code defining the type of initial privilege of this object; see text
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>initprivs</structfield> <type>aclitem[]</type>
      </para>
      <para>
       The initial access privileges; see
       <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-language">
  <title><structname>pg_language</structname></title>

  <indexterm zone="catalog-pg-language">
   <primary>pg_language</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_language</structname> registers
   languages in which you can write functions or stored procedures.
   See <xref linkend="sql-createlanguage"/>
   and <xref linkend="xplang"/> for more information about language handlers.
  </para>

  <table>
   <title><structname>pg_language</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lanname</structfield> <type>name</type>
      </para>
      <para>
       Name of the language
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lanowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the language
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lanispl</structfield> <type>bool</type>
      </para>
      <para>
       This is false for internal languages (such as
       <acronym>SQL</acronym>) and true for user-defined languages.
       Currently, <application>pg_dump</application> still uses this
       to determine which languages need to be dumped, but this might be
       replaced by a different mechanism in the future.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lanpltrusted</structfield> <type>bool</type>
      </para>
      <para>
       True if this is a trusted language, which means that it is believed
       not to grant access to anything outside the normal SQL execution
       environment.  Only superusers can create functions in untrusted
       languages.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lanplcallfoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       For noninternal languages this references the language
       handler, which is a special function that is responsible for
       executing all functions that are written in the particular
       language. Zero for internal languages.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>laninline</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       This references a function that is responsible for executing
       <quote>inline</quote> anonymous code blocks
       (<xref linkend="sql-do"/> blocks).
       Zero if inline blocks are not supported.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lanvalidator</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       This references a language validator function that is responsible
       for checking the syntax and validity of new functions when they
       are created.  Zero if no validator is provided.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lanacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-largeobject">
  <title><structname>pg_largeobject</structname></title>

  <indexterm zone="catalog-pg-largeobject">
   <primary>pg_largeobject</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_largeobject</structname> holds the data making up
   <quote>large objects</quote>.  A large object is identified by an OID
   assigned when it is created.  Each large object is broken into
   segments or <quote>pages</quote> small enough to be conveniently stored as rows
   in <structname>pg_largeobject</structname>.
   The amount of data per page is defined to be <symbol>LOBLKSIZE</symbol> (which is currently
   <literal>BLCKSZ/4</literal>, or typically 2 kB).
  </para>

  <para>
   Prior to <productname>PostgreSQL</productname> 9.0, there was no permission structure
   associated with large objects.  As a result,
   <structname>pg_largeobject</structname> was publicly readable and could be
   used to obtain the OIDs (and contents) of all large objects in the system.
   This is no longer the case; use
   <link linkend="catalog-pg-largeobject-metadata"><structname>pg_largeobject_metadata</structname></link>
   to obtain a list of large object OIDs.
  </para>

  <table>
   <title><structname>pg_largeobject</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>loid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-largeobject-metadata"><structname>pg_largeobject_metadata</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Identifier of the large object that includes this page
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pageno</structfield> <type>int4</type>
      </para>
      <para>
       Page number of this page within its large object
       (counting from zero)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>data</structfield> <type>bytea</type>
      </para>
      <para>
       Actual data stored in the large object.
       This will never be more than <symbol>LOBLKSIZE</symbol> bytes and might be less.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Each row of <structname>pg_largeobject</structname> holds data
   for one page of a large object, beginning at
   byte offset (<literal>pageno * LOBLKSIZE</literal>) within the object.  The implementation
   allows sparse storage: pages might be missing, and might be shorter than
   <literal>LOBLKSIZE</literal> bytes even if they are not the last page of the object.
   Missing regions within a large object read as zeroes.
  </para>

 </sect1>

 <sect1 id="catalog-pg-largeobject-metadata">
  <title><structname>pg_largeobject_metadata</structname></title>

  <indexterm zone="catalog-pg-largeobject-metadata">
   <primary>pg_largeobject_metadata</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_largeobject_metadata</structname>
   holds metadata associated with large objects.  The actual large object
   data is stored in
   <link linkend="catalog-pg-largeobject"><structname>pg_largeobject</structname></link>.
  </para>

  <table>
   <title><structname>pg_largeobject_metadata</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lomowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the large object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lomacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-namespace">
  <title><structname>pg_namespace</structname></title>

  <indexterm zone="catalog-pg-namespace">
   <primary>pg_namespace</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_namespace</structname> stores namespaces.
   A namespace is the structure underlying SQL schemas: each namespace
   can have a separate collection of relations, types, etc. without name
   conflicts.
  </para>

  <table>
   <title><structname>pg_namespace</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>nspname</structfield> <type>name</type>
      </para>
      <para>
       Name of the namespace
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>nspowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the namespace
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>nspacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-opclass">
  <title><structname>pg_opclass</structname></title>

  <indexterm zone="catalog-pg-opclass">
   <primary>pg_opclass</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_opclass</structname> defines
   index access method operator classes.  Each operator class defines
   semantics for index columns of a particular data type and a particular
   index access method.  An operator class essentially specifies that a
   particular operator family is applicable to a particular indexable column
   data type.  The set of operators from the family that are actually usable
   with the indexed column are whichever ones accept the column's data type
   as their left-hand input.
  </para>

  <para>
   Operator classes are described at length in <xref linkend="xindex"/>.
  </para>

  <table>
   <title><structname>pg_opclass</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opcmethod</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-am"><structname>pg_am</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Index access method operator class is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opcname</structfield> <type>name</type>
      </para>
      <para>
       Name of this operator class
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opcnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Namespace of this operator class
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opcowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the operator class
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opcfamily</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Operator family containing the operator class
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opcintype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Data type that the operator class indexes
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opcdefault</structfield> <type>bool</type>
      </para>
      <para>
       True if this operator class is the default for <structfield>opcintype</structfield>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opckeytype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Type of data stored in index, or zero if same as <structfield>opcintype</structfield>
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   An operator class's <structfield>opcmethod</structfield> must match the
   <structfield>opfmethod</structfield> of its containing operator family.
   Also, there must be no more than one <structname>pg_opclass</structname>
   row having <structfield>opcdefault</structfield> true for any given combination of
   <structfield>opcmethod</structfield> and <structfield>opcintype</structfield>.
  </para>

 </sect1>


 <sect1 id="catalog-pg-operator">
  <title><structname>pg_operator</structname></title>

  <indexterm zone="catalog-pg-operator">
   <primary>pg_operator</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_operator</structname> stores information about operators.
   See <xref linkend="sql-createoperator"/>
   and <xref linkend="xoper"/> for more information.
  </para>

  <table>
   <title><structname>pg_operator</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprname</structfield> <type>name</type>
      </para>
      <para>
       Name of the operator
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this operator
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the operator
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprkind</structfield> <type>char</type>
      </para>
      <para>
       <literal>b</literal> = infix operator (<quote>both</quote>),
       or <literal>l</literal> = prefix operator (<quote>left</quote>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprcanmerge</structfield> <type>bool</type>
      </para>
      <para>
       This operator supports merge joins
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprcanhash</structfield> <type>bool</type>
      </para>
      <para>
       This operator supports hash joins
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprleft</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Type of the left operand (zero for a prefix operator)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprright</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Type of the right operand
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprresult</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Type of the result
       (zero for a not-yet-defined <quote>shell</quote> operator)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprcom</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Commutator of this operator (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprnegate</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Negator of this operator (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprcode</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Function that implements this operator
       (zero for a not-yet-defined <quote>shell</quote> operator)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprrest</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Restriction selectivity estimation function for this operator
       (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oprjoin</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Join selectivity estimation function for this operator
       (zero if none)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-opfamily">
  <title><structname>pg_opfamily</structname></title>

  <indexterm zone="catalog-pg-opfamily">
   <primary>pg_opfamily</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_opfamily</structname> defines operator families.
   Each operator family is a collection of operators and associated
   support routines that implement the semantics specified for a particular
   index access method.  Furthermore, the operators in a family are all
   <quote>compatible</quote>, in a way that is specified by the access method.
   The operator family concept allows cross-data-type operators to be used
   with indexes and to be reasoned about using knowledge of access method
   semantics.
  </para>

  <para>
   Operator families are described at length in <xref linkend="xindex"/>.
  </para>

  <table>
   <title><structname>pg_opfamily</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opfmethod</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-am"><structname>pg_am</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Index access method operator family is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opfname</structfield> <type>name</type>
      </para>
      <para>
       Name of this operator family
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opfnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Namespace of this operator family
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>opfowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the operator family
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The majority of the information defining an operator family is not in its
   <structname>pg_opfamily</structname> row, but in the associated rows in
   <link linkend="catalog-pg-amop"><structname>pg_amop</structname></link>,
   <link linkend="catalog-pg-amproc"><structname>pg_amproc</structname></link>,
   and
   <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.
  </para>

 </sect1>


 <sect1 id="catalog-pg-partitioned-table">
  <title><structname>pg_partitioned_table</structname></title>

  <indexterm zone="catalog-pg-partitioned-table">
   <primary>pg_partitioned_table</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_partitioned_table</structname> stores
   information about how tables are partitioned.
  </para>

  <table>
   <title><structname>pg_partitioned_table</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the <link linkend="catalog-pg-class"><structname>pg_class</structname></link> entry for this partitioned table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partstrat</structfield> <type>char</type>
      </para>
      <para>
       Partitioning strategy; <literal>h</literal> = hash partitioned table,
       <literal>l</literal> = list partitioned table, <literal>r</literal> = range partitioned table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partnatts</structfield> <type>int2</type>
      </para>
      <para>
       The number of columns in the partition key
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partdefid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the <link linkend="catalog-pg-class"><structname>pg_class</structname></link> entry for the default partition
       of this partitioned table, or zero if this partitioned table does not
       have a default partition
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partattrs</structfield> <type>int2vector</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attnum</structfield>)
      </para>
      <para>
       This is an array of <structfield>partnatts</structfield> values that
       indicate which table columns are part of the partition key.  For
       example, a value of <literal>1 3</literal> would mean that the first
       and the third table columns make up the partition key.  A zero in this
       array indicates that the corresponding partition key column is an
       expression, rather than a simple column reference.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partclass</structfield> <type>oidvector</type>
       (references <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       For each column in the partition key, this contains the OID of the
       operator class to use.  See
       <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link> for details.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partcollation</structfield> <type>oidvector</type>
       (references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       For each column in the partition key, this contains the OID of the
       collation to use for partitioning, or zero if the column is not
       of a collatable data type.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partexprs</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Expression trees (in <function>nodeToString()</function>
       representation) for partition key columns that are not simple column
       references.  This is a list with one element for each zero
       entry in <structfield>partattrs</structfield>.  Null if all partition key columns
       are simple references.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-policy">
  <title><structname>pg_policy</structname></title>

  <indexterm zone="catalog-pg-policy">
   <primary>pg_policy</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_policy</structname> stores row-level
   security policies for tables.  A policy includes the kind of
   command that it applies to (possibly all commands), the roles that it
   applies to, the expression to be added as a security-barrier
   qualification to queries that include the table, and the expression
   to be added as a <literal>WITH CHECK</literal> option for queries that attempt to
   add new records to the table.
  </para>

  <table>
   <title><structname>pg_policy</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>polname</structfield> <type>name</type>
      </para>
      <para>
       The name of the policy
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>polrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The table to which the policy applies
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>polcmd</structfield> <type>char</type>
      </para>
      <para>
       The command type to which the policy is applied:
       <literal>r</literal> for <xref linkend="sql-select"/>,
       <literal>a</literal> for <xref linkend="sql-insert"/>,
       <literal>w</literal> for <xref linkend="sql-update"/>,
       <literal>d</literal> for <xref linkend="sql-delete"/>,
       or <literal>*</literal> for all
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>polpermissive</structfield> <type>bool</type>
      </para>
      <para>
       Is the policy permissive or restrictive?
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>polroles</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The roles to which the policy is applied;
       zero means <literal>PUBLIC</literal>
       (and normally appears alone in the array)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>polqual</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       The expression tree to be added to the security barrier qualifications for queries that use the table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>polwithcheck</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       The expression tree to be added to the WITH CHECK qualifications for queries that attempt to add rows to the table
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <note>
   <para>
    Policies stored in <structname>pg_policy</structname> are applied only when
    <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relrowsecurity</structfield> is set for
    their table.
   </para>
  </note>

 </sect1>

 <sect1 id="catalog-pg-proc">
  <title><structname>pg_proc</structname></title>

  <indexterm zone="catalog-pg-proc">
   <primary>pg_proc</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_proc</structname> stores information about
   functions, procedures, aggregate functions, and window functions
   (collectively also known as routines).  See <xref
   linkend="sql-createfunction"/>, <xref linkend="sql-createprocedure"/>, and
   <xref linkend="xfunc"/> for more information.
  </para>

  <para>
   If <structfield>prokind</structfield> indicates that the entry is for an
   aggregate function, there should be a matching row in
   <link linkend="catalog-pg-aggregate"><structfield>pg_aggregate</structfield></link>.
  </para>

  <table>
   <title><structname>pg_proc</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proname</structfield> <type>name</type>
      </para>
      <para>
       Name of the function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pronamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prolang</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-language"><structname>pg_language</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Implementation language or call interface of this function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>procost</structfield> <type>float4</type>
      </para>
      <para>
       Estimated execution cost (in units of
       <xref linkend="guc-cpu-operator-cost"/>); if <structfield>proretset</structfield>,
       this is cost per row returned
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prorows</structfield> <type>float4</type>
      </para>
      <para>
       Estimated number of result rows (zero if not <structfield>proretset</structfield>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>provariadic</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Data type of the variadic array parameter's elements,
       or zero if the function does not have a variadic parameter
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prosupport</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Planner support function for this function
       (see <xref linkend="xfunc-optimization"/>), or zero if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prokind</structfield> <type>char</type>
      </para>
      <para>
       <literal>f</literal> for a normal function, <literal>p</literal>
       for a procedure, <literal>a</literal> for an aggregate function, or
       <literal>w</literal> for a window function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prosecdef</structfield> <type>bool</type>
      </para>
      <para>
       Function is a security definer (i.e., a <quote>setuid</quote>
       function)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proleakproof</structfield> <type>bool</type>
      </para>
      <para>
       The function has no side effects.  No information about the
       arguments is conveyed except via the return value.  Any function
       that might throw an error depending on the values of its arguments
       is not leak-proof.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proisstrict</structfield> <type>bool</type>
      </para>
      <para>
       Function returns null if any call argument is null.  In that
       case the function won't actually be called at all.  Functions
       that are not <quote>strict</quote> must be prepared to handle
       null inputs.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proretset</structfield> <type>bool</type>
      </para>
      <para>
       Function returns a set (i.e., multiple values of the specified
       data type)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>provolatile</structfield> <type>char</type>
      </para>
      <para>
       <structfield>provolatile</structfield> tells whether the function's
       result depends only on its input arguments, or is affected by outside
       factors.
       It is <literal>i</literal> for <quote>immutable</quote> functions,
       which always deliver the same result for the same inputs.
       It is <literal>s</literal> for <quote>stable</quote> functions,
       whose results (for fixed inputs) do not change within a scan.
       It is <literal>v</literal> for <quote>volatile</quote> functions,
       whose results might change at any time.  (Use <literal>v</literal> also
       for functions with side-effects, so that calls to them cannot get
       optimized away.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proparallel</structfield> <type>char</type>
      </para>
      <para>
       <structfield>proparallel</structfield> tells whether the function
       can be safely run in parallel mode.
       It is <literal>s</literal> for functions which are safe to run in
       parallel mode without restriction.
       It is <literal>r</literal> for functions which can be run in parallel
       mode, but their execution is restricted to the parallel group leader;
       parallel worker processes cannot invoke these functions.
       It is <literal>u</literal> for functions which are unsafe in parallel
       mode; the presence of such a function forces a serial execution plan.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pronargs</structfield> <type>int2</type>
      </para>
      <para>
       Number of input arguments
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pronargdefaults</structfield> <type>int2</type>
      </para>
      <para>
       Number of arguments that have defaults
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prorettype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Data type of the return value
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proargtypes</structfield> <type>oidvector</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       An array of the data types of the function arguments.  This includes
       only input arguments (including <literal>INOUT</literal> and
       <literal>VARIADIC</literal> arguments), and thus represents
       the call signature of the function.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proallargtypes</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       An array of the data types of the function arguments.  This includes
       all arguments (including <literal>OUT</literal> and
       <literal>INOUT</literal> arguments); however, if all the
       arguments are <literal>IN</literal> arguments, this field will be null.
       Note that subscripting is 1-based, whereas for historical reasons
       <structfield>proargtypes</structfield> is subscripted from 0.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proargmodes</structfield> <type>char[]</type>
      </para>
      <para>
       An array of the modes of the function arguments, encoded as
       <literal>i</literal> for <literal>IN</literal> arguments,
       <literal>o</literal> for <literal>OUT</literal> arguments,
       <literal>b</literal> for <literal>INOUT</literal> arguments,
       <literal>v</literal> for <literal>VARIADIC</literal> arguments,
       <literal>t</literal> for <literal>TABLE</literal> arguments.
       If all the arguments are <literal>IN</literal> arguments,
       this field will be null.
       Note that subscripts correspond to positions of
       <structfield>proallargtypes</structfield> not <structfield>proargtypes</structfield>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proargnames</structfield> <type>text[]</type>
      </para>
      <para>
       An array of the names of the function arguments.
       Arguments without a name are set to empty strings in the array.
       If none of the arguments have a name, this field will be null.
       Note that subscripts correspond to positions of
       <structfield>proallargtypes</structfield> not <structfield>proargtypes</structfield>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proargdefaults</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Expression trees (in <function>nodeToString()</function> representation)
       for default values.  This is a list with
       <structfield>pronargdefaults</structfield> elements, corresponding to the last
       <replaceable>N</replaceable> <emphasis>input</emphasis> arguments (i.e., the last
       <replaceable>N</replaceable> <structfield>proargtypes</structfield> positions).
       If none of the arguments have defaults, this field will be null.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>protrftypes</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       An array of the argument/result data type(s) for which to apply
       transforms (from the function's <literal>TRANSFORM</literal>
       clause).  Null if none.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prosrc</structfield> <type>text</type>
      </para>
      <para>
       This tells the function handler how to invoke the function.  It
       might be the actual source code of the function for interpreted
       languages, a link symbol, a file name, or just about anything
       else, depending on the implementation language/call convention.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>probin</structfield> <type>text</type>
      </para>
      <para>
       Additional information about how to invoke the function.
       Again, the interpretation is language-specific.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prosqlbody</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Pre-parsed SQL function body.  This is used for SQL-language
       functions when the body is given in SQL-standard notation
       rather than as a string literal.  It's null in other cases.
       </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proconfig</structfield> <type>text[]</type>
      </para>
      <para>
       Function's local settings for run-time configuration variables
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>proacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   For compiled functions, both built-in and dynamically loaded,
   <structfield>prosrc</structfield> contains the function's C-language
   name (link symbol).
   For SQL-language functions, <structfield>prosrc</structfield> contains
   the function's source text if that is specified as a string literal;
   but if the function body is specified in SQL-standard style,
   <structfield>prosrc</structfield> is unused (typically it's an empty
   string) and <structfield>prosqlbody</structfield> contains the
   pre-parsed definition.
   For all other currently-known language types,
   <structfield>prosrc</structfield> contains the function's source
   text.  <structfield>probin</structfield> is null except for
   dynamically-loaded C functions, for which it gives the name of the
   shared library file containing the function.
  </para>

 </sect1>

 <sect1 id="catalog-pg-publication">
  <title><structname>pg_publication</structname></title>

  <indexterm zone="catalog-pg-publication">
   <primary>pg_publication</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_publication</structname> contains all
   publications created in the database.  For more on publications see
   <xref linkend="logical-replication-publication"/>.
  </para>

  <table>
   <title><structname>pg_publication</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pubname</structfield> <type>name</type>
      </para>
      <para>
       Name of the publication
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pubowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the publication
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>puballtables</structfield> <type>bool</type>
      </para>
      <para>
       If true, this publication automatically includes all tables
       in the database, including any that will be created in the future.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pubinsert</structfield> <type>bool</type>
      </para>
      <para>
       If true, <xref linkend="sql-insert"/> operations are replicated for
       tables in the publication.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pubupdate</structfield> <type>bool</type>
      </para>
      <para>
       If true, <xref linkend="sql-update"/> operations are replicated for
       tables in the publication.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pubdelete</structfield> <type>bool</type>
      </para>
      <para>
       If true, <xref linkend="sql-delete"/> operations are replicated for
       tables in the publication.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pubtruncate</structfield> <type>bool</type>
      </para>
      <para>
       If true, <xref linkend="sql-truncate"/> operations are replicated for
       tables in the publication.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pubviaroot</structfield> <type>bool</type>
      </para>
      <para>
       If true, operations on a leaf partition are replicated using the
       identity and schema of its topmost partitioned ancestor mentioned in the
       publication instead of its own.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="catalog-pg-publication-rel">
  <title><structname>pg_publication_rel</structname></title>

  <indexterm zone="catalog-pg-publication-rel">
   <primary>pg_publication_rel</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_publication_rel</structname> contains the
   mapping between relations and publications in the database.  This is a
   many-to-many mapping.  See also <xref linkend="view-pg-publication-tables"/>
   for a more user-friendly view of this information.
  </para>

  <table>
   <title><structname>pg_publication_rel</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prpubid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-publication"><structname>pg_publication</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Reference to publication
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Reference to relation
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="catalog-pg-range">
  <title><structname>pg_range</structname></title>

  <indexterm zone="catalog-pg-range">
   <primary>pg_range</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_range</structname> stores information about
   range types.  This is in addition to the types' entries in
   <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.
  </para>

  <table>
   <title><structname>pg_range</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rngtypid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the range type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rngsubtype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the element type (subtype) of this range type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rngmultitypid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the multirange type for this range type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rngcollation</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the collation used for range comparisons, or zero if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rngsubopc</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the subtype's operator class used for range comparisons
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rngcanonical</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the function to convert a range value into canonical form,
       or zero if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rngsubdiff</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the function to return the difference between two element
       values as <type>double precision</type>, or zero if none
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   <structfield>rngsubopc</structfield> (plus <structfield>rngcollation</structfield>, if the
   element type is collatable) determines the sort ordering used by the range
   type.  <structfield>rngcanonical</structfield> is used when the element type is
   discrete.  <structfield>rngsubdiff</structfield> is optional but should be supplied to
   improve performance of GiST indexes on the range type.
  </para>

 </sect1>

 <sect1 id="catalog-pg-replication-origin">
  <title><structname>pg_replication_origin</structname></title>

  <indexterm zone="catalog-pg-replication-origin">
   <primary>pg_replication_origin</primary>
  </indexterm>

  <para>
   The <structname>pg_replication_origin</structname> catalog contains
   all replication origins created.  For more on replication origins
   see <xref linkend="replication-origins"/>.
  </para>

  <para>
   Unlike most system catalogs, <structname>pg_replication_origin</structname>
   is shared across all databases of a cluster: there is only one copy
   of <structname>pg_replication_origin</structname> per cluster, not one per
   database.
  </para>

  <table>
   <title><structname>pg_replication_origin</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>roident</structfield> <type>oid</type>
      </para>
      <para>
       A unique, cluster-wide identifier for the replication
       origin. Should never leave the system.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>roname</structfield> <type>text</type>
      </para>
      <para>
       The external, user defined, name of a replication
       origin.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="catalog-pg-rewrite">
  <title><structname>pg_rewrite</structname></title>

  <indexterm zone="catalog-pg-rewrite">
   <primary>pg_rewrite</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_rewrite</structname> stores rewrite rules for tables and views.
  </para>

  <table>
   <title><structname>pg_rewrite</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rulename</structfield> <type>name</type>
      </para>
      <para>
       Rule name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ev_class</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The table this rule is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ev_type</structfield> <type>char</type>
      </para>
      <para>
       Event type that the rule is for: 1 = <xref linkend="sql-select"/>, 2 =
       <xref linkend="sql-update"/>, 3 = <xref linkend="sql-insert"/>, 4 =
       <xref linkend="sql-delete"/>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ev_enabled</structfield> <type>char</type>
      </para>
      <para>
       Controls in which <xref linkend="guc-session-replication-role"/> modes
       the rule fires.
       <literal>O</literal> = rule fires in <quote>origin</quote> and <quote>local</quote> modes,
       <literal>D</literal> = rule is disabled,
       <literal>R</literal> = rule fires in <quote>replica</quote> mode,
       <literal>A</literal> = rule fires always.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>is_instead</structfield> <type>bool</type>
      </para>
      <para>
       True if the rule is an <literal>INSTEAD</literal> rule
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ev_qual</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Expression tree (in the form of a
       <function>nodeToString()</function> representation) for the
       rule's qualifying condition
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ev_action</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Query tree (in the form of a
       <function>nodeToString()</function> representation) for the
       rule's action
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <note>
   <para>
    <literal>pg_class.relhasrules</literal>
    must be true if a table has any rules in this catalog.
   </para>
  </note>

 </sect1>

 <sect1 id="catalog-pg-seclabel">
  <title><structname>pg_seclabel</structname></title>

  <indexterm zone="catalog-pg-seclabel">
   <primary>pg_seclabel</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_seclabel</structname> stores security
   labels on database objects.  Security labels can be manipulated
   with the <link linkend="sql-security-label"><command>SECURITY LABEL</command></link> command.  For an easier
   way to view security labels, see <xref linkend="view-pg-seclabels"/>.
  </para>

  <para>
   See also <link linkend="catalog-pg-shseclabel"><structname>pg_shseclabel</structname></link>,
   which performs a similar function for security labels of database objects
   that are shared across a database cluster.
  </para>

  <table>
   <title><structname>pg_seclabel</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objoid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the object this security label pertains to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog this object appears in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objsubid</structfield> <type>int4</type>
      </para>
      <para>
       For a security label on a table column, this is the column number (the
       <structfield>objoid</structfield> and <structfield>classoid</structfield> refer to
       the table itself).  For all other object types, this column is
       zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>provider</structfield> <type>text</type>
      </para>
      <para>
       The label provider associated with this label.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>label</structfield> <type>text</type>
      </para>
      <para>
       The security label applied to this object.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="catalog-pg-sequence">
  <title><structname>pg_sequence</structname></title>

  <indexterm zone="catalog-pg-sequence">
   <primary>pg_sequence</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_sequence</structname> contains information about
   sequences.  Some of the information about sequences, such as the name and
   the schema, is in
   <link linkend="catalog-pg-class"><structname>pg_class</structname></link>
  </para>

  <table>
   <title><structname>pg_sequence</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the <link linkend="catalog-pg-class"><structname>pg_class</structname></link> entry for this sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqtypid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Data type of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqstart</structfield> <type>int8</type>
      </para>
      <para>
       Start value of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqincrement</structfield> <type>int8</type>
      </para>
      <para>
       Increment value of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqmax</structfield> <type>int8</type>
      </para>
      <para>
       Maximum value of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqmin</structfield> <type>int8</type>
      </para>
      <para>
       Minimum value of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqcache</structfield> <type>int8</type>
      </para>
      <para>
       Cache size of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqcycle</structfield> <type>bool</type>
      </para>
      <para>
       Whether the sequence cycles
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="catalog-pg-shdepend">
  <title><structname>pg_shdepend</structname></title>

  <indexterm zone="catalog-pg-shdepend">
   <primary>pg_shdepend</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_shdepend</structname> records the
   dependency relationships between database objects and shared objects,
   such as roles.  This information allows
   <productname>PostgreSQL</productname> to ensure that those objects are
   unreferenced before attempting to delete them.
  </para>

  <para>
   See also <link linkend="catalog-pg-depend"><structname>pg_depend</structname></link>,
   which performs a similar function for dependencies involving objects
   within a single database.
  </para>

  <para>
   Unlike most system catalogs, <structname>pg_shdepend</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_shdepend</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_shdepend</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dbid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-database"><structname>pg_database</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the database the dependent object is in,
       or zero for a shared object
       or a <symbol>SHARED_DEPENDENCY_PIN</symbol> entry
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog the dependent object is in,
       or zero for a <symbol>SHARED_DEPENDENCY_PIN</symbol> entry
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the specific dependent object,
       or zero for a <symbol>SHARED_DEPENDENCY_PIN</symbol> entry
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objsubid</structfield> <type>int4</type>
      </para>
      <para>
       For a table column, this is the column number (the
       <structfield>objid</structfield> and <structfield>classid</structfield> refer to the
       table itself).  For all other object types, this column is zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>refclassid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog the referenced object is in
       (must be a shared catalog)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>refobjid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the specific referenced object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>deptype</structfield> <type>char</type>
      </para>
      <para>
       A code defining the specific semantics of this dependency relationship; see text
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   In all cases, a <structname>pg_shdepend</structname> entry indicates that
   the referenced object cannot be dropped without also dropping the dependent
   object.  However, there are several subflavors identified by
   <structfield>deptype</structfield>:

   <variablelist>
    <varlistentry>
     <term><symbol>SHARED_DEPENDENCY_OWNER</symbol> (<literal>o</literal>)</term>
     <listitem>
      <para>
       The referenced object (which must be a role) is the owner of the
       dependent object.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SHARED_DEPENDENCY_ACL</symbol> (<literal>a</literal>)</term>
     <listitem>
      <para>
       The referenced object (which must be a role) is mentioned in the
       ACL (access control list, i.e., privileges list) of the
       dependent object.  (A <symbol>SHARED_DEPENDENCY_ACL</symbol> entry is
       not made for the owner of the object, since the owner will have
       a <symbol>SHARED_DEPENDENCY_OWNER</symbol> entry anyway.)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SHARED_DEPENDENCY_POLICY</symbol> (<literal>r</literal>)</term>
     <listitem>
      <para>
       The referenced object (which must be a role) is mentioned as the
       target of a dependent policy object.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SHARED_DEPENDENCY_PIN</symbol> (<literal>p</literal>)</term>
     <listitem>
      <para>
       There is no dependent object; this type of entry is a signal
       that the system itself depends on the referenced object, and so
       that object must never be deleted.  Entries of this type are
       created only by <application>initdb</application>.  The columns for the
       dependent object contain zeroes.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SHARED_DEPENDENCY_TABLESPACE</symbol> (<literal>t</literal>)</term>
     <listitem>
      <para>
       The referenced object (which must be a tablespace) is mentioned as
       the tablespace for a relation that doesn't have storage.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><symbol>SHARED_DEPENDENCY_PROFILE</symbol> (<literal>t</literal>)</term>
     <listitem>
      <para>
       The referenced object (which must be a profile) is mentioned as
       the profile for a role using.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>

   Other dependency flavors might be needed in future.  Note in particular
   that the current definition only supports roles and tablespaces as referenced
   objects.
  </para>

 </sect1>

 <sect1 id="catalog-pg-shdescription">
  <title><structname>pg_shdescription</structname></title>

  <indexterm zone="catalog-pg-shdescription">
   <primary>pg_shdescription</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_shdescription</structname> stores optional
   descriptions (comments) for shared database objects.  Descriptions can be
   manipulated with the <link linkend="sql-comment"><command>COMMENT</command></link> command and viewed with
   <application>psql</application>'s <literal>\d</literal> commands.
  </para>

  <para>
   See also <link linkend="catalog-pg-description"><structname>pg_description</structname></link>,
   which performs a similar function for descriptions involving objects
   within a single database.
  </para>

  <para>
   Unlike most system catalogs, <structname>pg_shdescription</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_shdescription</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_shdescription</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objoid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the object this description pertains to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog this object appears in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>description</structfield> <type>text</type>
      </para>
      <para>
       Arbitrary text that serves as the description of this object
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="catalog-pg-shseclabel">
  <title><structname>pg_shseclabel</structname></title>

  <indexterm zone="catalog-pg-shseclabel">
   <primary>pg_shseclabel</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_shseclabel</structname> stores security
   labels on shared database objects.  Security labels can be manipulated
   with the <link linkend="sql-security-label"><command>SECURITY LABEL</command></link> command.  For an easier
   way to view security labels, see <xref linkend="view-pg-seclabels"/>.
  </para>

  <para>
   See also <link linkend="catalog-pg-seclabel"><structname>pg_seclabel</structname></link>,
   which performs a similar function for security labels involving objects
   within a single database.
  </para>

  <para>
   Unlike most system catalogs, <structname>pg_shseclabel</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_shseclabel</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_shseclabel</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objoid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the object this security label pertains to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog this object appears in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>provider</structfield> <type>text</type>
      </para>
      <para>
       The label provider associated with this label.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>label</structfield> <type>text</type>
      </para>
      <para>
       The security label applied to this object.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="catalog-pg-statistic">
  <title><structname>pg_statistic</structname></title>

  <indexterm zone="catalog-pg-statistic">
   <primary>pg_statistic</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_statistic</structname> stores
   statistical data about the contents of the database.  Entries are
   created by <link linkend="sql-analyze"><command>ANALYZE</command></link>
   and subsequently used by the query planner.  Note that all the
   statistical data is inherently approximate, even assuming that it
   is up-to-date.
  </para>

  <para>
   Normally there is one entry, with <structfield>stainherit</structfield> =
   <literal>false</literal>, for each table column that has been analyzed.
   If the table has inheritance children, a second entry with
   <structfield>stainherit</structfield> = <literal>true</literal> is also created.  This row
   represents the column's statistics over the inheritance tree, i.e.,
   statistics for the data you'd see with
   <literal>SELECT <replaceable>column</replaceable> FROM <replaceable>table</replaceable>*</literal>,
   whereas the <structfield>stainherit</structfield> = <literal>false</literal> row represents
   the results of
   <literal>SELECT <replaceable>column</replaceable> FROM ONLY <replaceable>table</replaceable></literal>.
  </para>

  <para>
   <structname>pg_statistic</structname> also stores statistical data about
   the values of index expressions.  These are described as if they were
   actual data columns; in particular, <structfield>starelid</structfield>
   references the index.  No entry is made for an ordinary non-expression
   index column, however, since it would be redundant with the entry
   for the underlying table column.  Currently, entries for index expressions
   always have <structfield>stainherit</structfield> = <literal>false</literal>.
  </para>

  <para>
   Since different kinds of statistics might be appropriate for different
   kinds of data, <structname>pg_statistic</structname> is designed not
   to assume very much about what sort of statistics it stores.  Only
   extremely general statistics (such as nullness) are given dedicated
   columns in <structname>pg_statistic</structname>.  Everything else
   is stored in <quote>slots</quote>, which are groups of associated columns
   whose content is identified by a code number in one of the slot's columns.
   For more information see
   <filename>src/include/catalog/pg_statistic.h</filename>.
  </para>

  <para>
   <structname>pg_statistic</structname> should not be readable by the
   public, since even statistical information about a table's contents
   might be considered sensitive.  (Example: minimum and maximum values
   of a salary column might be quite interesting.)
   <link linkend="view-pg-stats"><structname>pg_stats</structname></link>
   is a publicly readable view on
   <structname>pg_statistic</structname> that only exposes information
   about those tables that are readable by the current user.
  </para>

  <table>
   <title><structname>pg_statistic</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>starelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The table or index that the described column belongs to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>staattnum</structfield> <type>int2</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attnum</structfield>)
      </para>
      <para>
       The number of the described column
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stainherit</structfield> <type>bool</type>
      </para>
      <para>
       If true, the stats include inheritance child columns, not just the
       values in the specified relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stanullfrac</structfield> <type>float4</type>
      </para>
      <para>
       The fraction of the column's entries that are null
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stawidth</structfield> <type>int4</type>
      </para>
      <para>
       The average stored width, in bytes, of nonnull entries
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stadistinct</structfield> <type>float4</type>
      </para>
      <para>
       The number of distinct nonnull data values in the column.
       A value greater than zero is the actual number of distinct values.
       A value less than zero is the negative of a multiplier for the number
       of rows in the table; for example, a column in which about 80% of the
       values are nonnull and each nonnull value appears about twice on
       average could be represented by <structfield>stadistinct</structfield> = -0.4.
       A zero value means the number of distinct values is unknown.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stakind<replaceable>N</replaceable></structfield> <type>int2</type>
      </para>
      <para>
       A code number indicating the kind of statistics stored in the
       <replaceable>N</replaceable>th <quote>slot</quote> of the
       <structname>pg_statistic</structname> row.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>staop<replaceable>N</replaceable></structfield> <type>oid</type>
       (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       An operator used to derive the statistics stored in the
       <replaceable>N</replaceable>th <quote>slot</quote>.  For example, a
       histogram slot would show the <literal>&lt;</literal> operator
       that defines the sort order of the data.
       Zero if the statistics kind does not require an operator.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stacoll<replaceable>N</replaceable></structfield> <type>oid</type>
       (references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The collation used to derive the statistics stored in the
       <replaceable>N</replaceable>th <quote>slot</quote>.  For example, a
       histogram slot for a collatable column would show the collation that
       defines the sort order of the data.  Zero for noncollatable data.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stanumbers<replaceable>N</replaceable></structfield> <type>float4[]</type>
      </para>
      <para>
       Numerical statistics of the appropriate kind for the
       <replaceable>N</replaceable>th <quote>slot</quote>, or null if the slot
       kind does not involve numerical values
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stavalues<replaceable>N</replaceable></structfield> <type>anyarray</type>
      </para>
      <para>
       Column data values of the appropriate kind for the
       <replaceable>N</replaceable>th <quote>slot</quote>, or null if the slot
       kind does not store any data values.  Each array's element
       values are actually of the specific column's data type, or a related
       type such as an array's element type, so there is no way to define
       these columns' type more specifically than <type>anyarray</type>.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="catalog-pg-statistic-ext">
  <title><structname>pg_statistic_ext</structname></title>

  <indexterm zone="catalog-pg-statistic-ext">
   <primary>pg_statistic_ext</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_statistic_ext</structname>
   holds definitions of extended planner statistics.
   Each row in this catalog corresponds to a <firstterm>statistics object</firstterm>
   created with <link linkend="sql-createstatistics"><command>CREATE STATISTICS</command></link>.
  </para>

  <table>
   <title><structname>pg_statistic_ext</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Table containing the columns described by this object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxname</structfield> <type>name</type>
      </para>
      <para>
       Name of the statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxstattarget</structfield> <type>int4</type>
      </para>
      <para>
       <structfield>stxstattarget</structfield> controls the level of detail
       of statistics accumulated for this statistics object by
       <link linkend="sql-analyze"><command>ANALYZE</command></link>.
       A zero value indicates that no statistics should be collected.
       A negative value says to use the maximum of the statistics targets of
       the referenced columns, if set, or the system default statistics target.
       Positive values of <structfield>stxstattarget</structfield>
       determine the target number of <quote>most common values</quote>
       to collect.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxkeys</structfield> <type>int2vector</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attnum</structfield>)
      </para>
      <para>
       An array of attribute numbers, indicating which table columns are
       covered by this statistics object;
       for example a value of <literal>1 3</literal> would
       mean that the first and the third table columns are covered
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxkind</structfield> <type>char[]</type>
      </para>
      <para>
       An array containing codes for the enabled statistics kinds;
       valid values are:
       <literal>d</literal> for n-distinct statistics,
       <literal>f</literal> for functional dependency statistics,
       <literal>m</literal> for most common values (MCV) list statistics, and
       <literal>e</literal> for expression statistics
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxexprs</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Expression trees (in <function>nodeToString()</function>
       representation) for statistics object attributes that are not simple
       column references.  This is a list with one element per expression.
       Null if all statistics object attributes are simple references.
      </para></entry>
     </row>

    </tbody>
   </tgroup>
  </table>

  <para>
   The <structname>pg_statistic_ext</structname> entry is filled in
   completely during <link linkend="sql-createstatistics"><command>CREATE STATISTICS</command></link>, but the actual
   statistical values are not computed then.
   Subsequent <link linkend="sql-analyze"><command>ANALYZE</command></link> commands compute the desired values
   and populate an entry in the
   <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
   catalog.
  </para>
 </sect1>

 <sect1 id="catalog-pg-statistic-ext-data">
  <title><structname>pg_statistic_ext_data</structname></title>

  <indexterm zone="catalog-pg-statistic-ext">
   <primary>pg_statistic_ext_data</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_statistic_ext_data</structname>
   holds data for extended planner statistics defined in
   <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>.
   Each row in this catalog corresponds to a <firstterm>statistics object</firstterm>
   created with <link linkend="sql-createstatistics"><command>CREATE STATISTICS</command></link>.
  </para>

  <para>
   Like <link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link>,
   <structname>pg_statistic_ext_data</structname> should not be
   readable by the public, since the contents might be considered sensitive.
   (Example: most common combinations of values in columns might be quite
   interesting.)
   <link linkend="view-pg-stats-ext"><structname>pg_stats_ext</structname></link>
   is a publicly readable view
   on <structname>pg_statistic_ext_data</structname> (after joining
   with <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>) that only exposes
   information about tables the current user owns.
  </para>

  <table>
   <title><structname>pg_statistic_ext_data</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Extended statistics object containing the definition for this data
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxdndistinct</structfield> <type>pg_ndistinct</type>
      </para>
      <para>
       N-distinct counts, serialized as <structname>pg_ndistinct</structname> type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxddependencies</structfield> <type>pg_dependencies</type>
      </para>
      <para>
       Functional dependency statistics, serialized
       as <structname>pg_dependencies</structname> type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxdmcv</structfield> <type>pg_mcv_list</type>
      </para>
      <para>
       MCV (most-common values) list statistics, serialized as
       <structname>pg_mcv_list</structname> type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stxdexpr</structfield> <type>pg_statistic[]</type>
      </para>
      <para>
       Per-expression statistics, serialized as an array of
       <structname>pg_statistic</structname> type
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="catalog-pg-subscription">
  <title><structname>pg_subscription</structname></title>

  <indexterm zone="catalog-pg-subscription">
   <primary>pg_subscription</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_subscription</structname> contains all existing
   logical replication subscriptions.  For more information about logical
   replication see <xref linkend="logical-replication"/>.
  </para>

  <para>
   Unlike most system catalogs, <structname>pg_subscription</structname> is
   shared across all databases of a cluster: there is only one copy
   of <structname>pg_subscription</structname> per cluster, not one per
   database.
  </para>

  <para>
   Access to the column <structfield>subconninfo</structfield> is revoked from
   normal users, because it could contain plain-text passwords.
  </para>

  <table>
   <title><structname>pg_subscription</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subdbid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-database"><structname>pg_database</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the database that the subscription resides in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subname</structfield> <type>name</type>
      </para>
      <para>
       Name of the subscription
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the subscription
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subenabled</structfield> <type>bool</type>
      </para>
      <para>
       If true, the subscription is enabled and should be replicating
      </para></entry>
     </row>

    <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subbinary</structfield> <type>bool</type>
      </para>
      <para>
       If true, the subscription will request that the publisher send data
       in binary format
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>substream</structfield> <type>bool</type>
      </para>
      <para>
       If true, the subscription will allow streaming of in-progress
       transactions
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subconninfo</structfield> <type>text</type>
      </para>
      <para>
       Connection string to the upstream database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subslotname</structfield> <type>name</type>
      </para>
      <para>
       Name of the replication slot in the upstream database (also used
       for the local replication origin name);
       null represents <literal>NONE</literal>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subsynccommit</structfield> <type>text</type>
      </para>
      <para>
       The <varname>synchronous_commit</varname>
       setting for the subscription's workers to use
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subpublications</structfield> <type>text[]</type>
      </para>
      <para>
       Array of subscribed publication names. These reference
       publications defined in the upstream database. For more on publications
       see <xref linkend="logical-replication-publication"/>.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="catalog-pg-subscription-rel">
  <title><structname>pg_subscription_rel</structname></title>

  <indexterm zone="catalog-pg-subscription-rel">
   <primary>pg_subscription_rel</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_subscription_rel</structname> contains the
   state for each replicated relation in each subscription.  This is a
   many-to-many mapping.
  </para>

  <para>
   This catalog only contains tables known to the subscription after running
   either <link linkend="sql-createsubscription"><command>CREATE SUBSCRIPTION</command></link> or
   <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION ... REFRESH
   PUBLICATION</command></link>.
  </para>

  <table>
   <title><structname>pg_subscription_rel</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srsubid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-subscription"><structname>pg_subscription</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Reference to subscription
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Reference to relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srsubstate</structfield> <type>char</type>
      </para>
      <para>
       State code:
       <literal>i</literal> = initialize,
       <literal>d</literal> = data is being copied,
       <literal>f</literal> = finished table copy,
       <literal>s</literal> = synchronized,
       <literal>r</literal> = ready (normal replication)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srsublsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Remote LSN of the state change used for synchronization coordination
       when in <literal>s</literal> or <literal>r</literal> states,
       otherwise null
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="catalog-pg-tablespace">
  <title><structname>pg_tablespace</structname></title>

  <indexterm zone="catalog-pg-tablespace">
   <primary>pg_tablespace</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_tablespace</structname> stores information
   about the available tablespaces.  Tables can be placed in particular
   tablespaces to aid administration of disk layout.
  </para>

  <para>
   Unlike most system catalogs, <structname>pg_tablespace</structname>
   is shared across all databases of a cluster: there is only one
   copy of <structname>pg_tablespace</structname> per cluster, not
   one per database.
  </para>

  <table>
   <title><structname>pg_tablespace</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>spcname</structfield> <type>name</type>
      </para>
      <para>
       Tablespace name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>spcowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the tablespace, usually the user who created it
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>spcacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>spcoptions</structfield> <type>text[]</type>
      </para>
      <para>
       Tablespace-level options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-transform">
  <title><structname>pg_transform</structname></title>

  <indexterm zone="catalog-pg-transform">
   <primary>pg_transform</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_transform</structname> stores information about
   transforms, which are a mechanism to adapt data types to procedural
   languages.  See <xref linkend="sql-createtransform"/> for more information.
  </para>

  <table>
   <title><structname>pg_transform</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>trftype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the data type this transform is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>trflang</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-language"><structname>pg_language</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the language this transform is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>trffromsql</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the function to use when converting the data type for input
       to the procedural language (e.g., function parameters).  Zero is stored
       if the default behavior should be used.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>trftosql</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the function to use when converting output from the
       procedural language (e.g., return values) to the data type.  Zero is
       stored if the default behavior should be used.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-trigger">
  <title><structname>pg_trigger</structname></title>

  <indexterm zone="catalog-pg-trigger">
   <primary>pg_trigger</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_trigger</structname> stores triggers on tables
   and views.
   See <xref linkend="sql-createtrigger"/>
   for more information.
  </para>

  <table>
   <title><structname>pg_trigger</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The table this trigger is on
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgparentid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Parent trigger that this trigger is cloned from (this happens when
       partitions are created or attached to a partitioned table);
       zero if not a clone
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgname</structfield> <type>name</type>
      </para>
      <para>
       Trigger name (must be unique among triggers of same table)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgfoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The function to be called
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgtype</structfield> <type>int2</type>
      </para>
      <para>
       Bit mask identifying trigger firing conditions
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgenabled</structfield> <type>char</type>
      </para>
      <para>
       Controls in which <xref linkend="guc-session-replication-role"/> modes
       the trigger fires.
       <literal>O</literal> = trigger fires in <quote>origin</quote> and <quote>local</quote> modes,
       <literal>D</literal> = trigger is disabled,
       <literal>R</literal> = trigger fires in <quote>replica</quote> mode,
       <literal>A</literal> = trigger fires always.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgisinternal</structfield> <type>bool</type>
      </para>
      <para>
       True if trigger is internally generated (usually, to enforce
       the constraint identified by <structfield>tgconstraint</structfield>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgconstrrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The table referenced by a referential integrity constraint
       (zero if trigger is not for a referential integrity constraint)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgconstrindid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The index supporting a unique, primary key, referential integrity,
       or exclusion constraint
       (zero if trigger is not for one of these types of constraint)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgconstraint</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The <link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link> entry associated with the trigger
       (zero if trigger is not for a constraint)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgdeferrable</structfield> <type>bool</type>
      </para>
      <para>
       True if constraint trigger is deferrable
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tginitdeferred</structfield> <type>bool</type>
      </para>
      <para>
       True if constraint trigger is initially deferred
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgnargs</structfield> <type>int2</type>
      </para>
      <para>
       Number of argument strings passed to trigger function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgattr</structfield> <type>int2vector</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attnum</structfield>)
      </para>
      <para>
       Column numbers, if trigger is column-specific; otherwise an
       empty array
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgargs</structfield> <type>bytea</type>
      </para>
      <para>
       Argument strings to pass to trigger, each NULL-terminated
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgqual</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       Expression tree (in <function>nodeToString()</function>
       representation) for the trigger's <literal>WHEN</literal> condition, or null
       if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgoldtable</structfield> <type>name</type>
      </para>
      <para>
       <literal>REFERENCING</literal> clause name for <literal>OLD TABLE</literal>,
       or null if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tgnewtable</structfield> <type>name</type>
      </para>
      <para>
       <literal>REFERENCING</literal> clause name for <literal>NEW TABLE</literal>,
       or null if none
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Currently, column-specific triggering is supported only for
   <literal>UPDATE</literal> events, and so <structfield>tgattr</structfield> is relevant
   only for that event type.  <structfield>tgtype</structfield> might
   contain bits for other event types as well, but those are presumed
   to be table-wide regardless of what is in <structfield>tgattr</structfield>.
  </para>

  <note>
   <para>
    When <structfield>tgconstraint</structfield> is nonzero,
    <structfield>tgconstrrelid</structfield>, <structfield>tgconstrindid</structfield>,
    <structfield>tgdeferrable</structfield>, and <structfield>tginitdeferred</structfield> are
    largely redundant with the referenced <link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link> entry.
    However, it is possible for a non-deferrable trigger to be associated
    with a deferrable constraint: foreign key constraints can have some
    deferrable and some non-deferrable triggers.
   </para>
  </note>

  <note>
   <para>
    <literal>pg_class.relhastriggers</literal>
    must be true if a relation has any triggers in this catalog.
   </para>
  </note>

 </sect1>


 <sect1 id="catalog-pg-ts-config">
  <title><structname>pg_ts_config</structname></title>

  <indexterm zone="catalog-pg-ts-config">
   <primary>pg_ts_config</primary>
  </indexterm>

  <para>
   The <structname>pg_ts_config</structname> catalog contains entries
   representing text search configurations.  A configuration specifies
   a particular text search parser and a list of dictionaries to use
   for each of the parser's output token types.  The parser is shown
   in the <structname>pg_ts_config</structname> entry, but the
   token-to-dictionary mapping is defined by subsidiary entries in <link
   linkend="catalog-pg-ts-config-map"><structname>pg_ts_config_map</structname></link>.
  </para>

  <para>
   <productname>PostgreSQL</productname>'s text search features are
   described at length in <xref linkend="textsearch"/>.
  </para>

  <table>
   <title><structname>pg_ts_config</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cfgname</structfield> <type>name</type>
      </para>
      <para>
       Text search configuration name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cfgnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this configuration
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cfgowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the configuration
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cfgparser</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-ts-parser"><structname>pg_ts_parser</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the text search parser for this configuration
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-ts-config-map">
  <title><structname>pg_ts_config_map</structname></title>

  <indexterm zone="catalog-pg-ts-config-map">
   <primary>pg_ts_config_map</primary>
  </indexterm>

  <para>
   The <structname>pg_ts_config_map</structname> catalog contains entries
   showing which text search dictionaries should be consulted, and in
   what order, for each output token type of each text search configuration's
   parser.
  </para>

  <para>
   <productname>PostgreSQL</productname>'s text search features are
   described at length in <xref linkend="textsearch"/>.
  </para>

  <table>
   <title><structname>pg_ts_config_map</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>mapcfg</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-ts-config"><structname>pg_ts_config</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the <link linkend="catalog-pg-ts-config"><structname>pg_ts_config</structname></link> entry owning this map entry
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>maptokentype</structfield> <type>int4</type>
      </para>
      <para>
       A token type emitted by the configuration's parser
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>mapseqno</structfield> <type>int4</type>
      </para>
      <para>
       Order in which to consult this entry (lower
       <structfield>mapseqno</structfield>s first)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>mapdict</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-ts-dict"><structname>pg_ts_dict</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the text search dictionary to consult
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-ts-dict">
  <title><structname>pg_ts_dict</structname></title>

  <indexterm zone="catalog-pg-ts-dict">
   <primary>pg_ts_dict</primary>
  </indexterm>

  <para>
   The <structname>pg_ts_dict</structname> catalog contains entries
   defining text search dictionaries.  A dictionary depends on a text
   search template, which specifies all the implementation functions
   needed; the dictionary itself provides values for the user-settable
   parameters supported by the template.  This division of labor allows
   dictionaries to be created by unprivileged users.  The parameters
   are specified by a text string <structfield>dictinitoption</structfield>,
   whose format and meaning vary depending on the template.
  </para>

  <para>
   <productname>PostgreSQL</productname>'s text search features are
   described at length in <xref linkend="textsearch"/>.
  </para>

  <table>
   <title><structname>pg_ts_dict</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dictname</structfield> <type>name</type>
      </para>
      <para>
       Text search dictionary name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dictnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this dictionary
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dictowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the dictionary
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dicttemplate</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-ts-template"><structname>pg_ts_template</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the text search template for this dictionary
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dictinitoption</structfield> <type>text</type>
      </para>
      <para>
       Initialization option string for the template
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-ts-parser">
  <title><structname>pg_ts_parser</structname></title>

  <indexterm zone="catalog-pg-ts-parser">
   <primary>pg_ts_parser</primary>
  </indexterm>

  <para>
   The <structname>pg_ts_parser</structname> catalog contains entries
   defining text search parsers.  A parser is responsible for splitting
   input text into lexemes and assigning a token type to each lexeme.
   Since a parser must be implemented by C-language-level functions,
   creation of new parsers is restricted to database superusers.
  </para>

  <para>
   <productname>PostgreSQL</productname>'s text search features are
   described at length in <xref linkend="textsearch"/>.
  </para>

  <table>
   <title><structname>pg_ts_parser</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prsname</structfield> <type>name</type>
      </para>
      <para>
       Text search parser name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prsnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this parser
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prsstart</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the parser's startup function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prstoken</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the parser's next-token function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prsend</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the parser's shutdown function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prsheadline</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the parser's headline function (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prslextype</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the parser's lextype function
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-ts-template">
  <title><structname>pg_ts_template</structname></title>

  <indexterm zone="catalog-pg-ts-template">
   <primary>pg_ts_template</primary>
  </indexterm>

  <para>
   The <structname>pg_ts_template</structname> catalog contains entries
   defining text search templates.  A template is the implementation
   skeleton for a class of text search dictionaries.
   Since a template must be implemented by C-language-level functions,
   creation of new templates is restricted to database superusers.
  </para>

  <para>
   <productname>PostgreSQL</productname>'s text search features are
   described at length in <xref linkend="textsearch"/>.
  </para>

  <table>
   <title><structname>pg_ts_template</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tmplname</structfield> <type>name</type>
      </para>
      <para>
       Text search template name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tmplnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this template
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tmplinit</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the template's initialization function (zero if none)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tmpllexize</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the template's lexize function
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="catalog-pg-type">
  <title><structname>pg_type</structname></title>

  <indexterm zone="catalog-pg-type">
   <primary>pg_type</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_type</structname> stores information about data
   types.  Base types and enum types (scalar types) are created with
   <link linkend="sql-createtype"><command>CREATE TYPE</command></link>, and
   domains with
   <link linkend="sql-createdomain"><command>CREATE DOMAIN</command></link>.
   A composite type is automatically created for each table in the database, to
   represent the row structure of the table.  It is also possible to create
   composite types with <command>CREATE TYPE AS</command>.
  </para>

  <table>
   <title><structname>pg_type</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typname</structfield> <type>name</type>
      </para>
      <para>
       Data type name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace that contains this type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the type
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typlen</structfield> <type>int2</type>
      </para>
      <para>
       For a fixed-size type, <structfield>typlen</structfield> is the number
       of bytes in the internal representation of the type.  But for a
       variable-length type, <structfield>typlen</structfield> is negative.
       -1 indicates a <quote>varlena</quote> type (one that has a length word),
       -2 indicates a null-terminated C string.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typbyval</structfield> <type>bool</type>
      </para>
      <para>
       <structfield>typbyval</structfield> determines whether internal
       routines pass a value of this type by value or by reference.
       <structfield>typbyval</structfield> had better be false if
       <structfield>typlen</structfield> is not 1, 2, or 4 (or 8 on machines
       where Datum is 8 bytes).
       Variable-length types are always passed by reference. Note that
       <structfield>typbyval</structfield> can be false even if the
       length would allow pass-by-value.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typtype</structfield> <type>char</type>
      </para>
      <para>
       <structfield>typtype</structfield> is
       <literal>b</literal> for a base type,
       <literal>c</literal> for a composite type (e.g., a table's row type),
       <literal>d</literal> for a domain,
       <literal>e</literal> for an enum type,
       <literal>p</literal> for a pseudo-type,
       <literal>r</literal> for a range type, or
       <literal>m</literal> for a multirange type.
       See also <structfield>typrelid</structfield> and
       <structfield>typbasetype</structfield>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typcategory</structfield> <type>char</type>
      </para>
      <para>
       <structfield>typcategory</structfield> is an arbitrary classification
       of data types that is used by the parser to determine which implicit
       casts should be <quote>preferred</quote>.
       See <xref linkend="catalog-typcategory-table"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typispreferred</structfield> <type>bool</type>
      </para>
      <para>
       True if the type is a preferred cast target within its
       <structfield>typcategory</structfield>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typisdefined</structfield> <type>bool</type>
      </para>
      <para>
       True if the type is defined, false if this is a placeholder
       entry for a not-yet-defined type.  When
       <structfield>typisdefined</structfield> is false, nothing
       except the type name, namespace, and OID can be relied on.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typdelim</structfield> <type>char</type>
      </para>
      <para>
       Character that separates two values of this type when parsing
       array input.  Note that the delimiter is associated with the array
       element data type, not the array data type.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typrelid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If this is a composite type (see
       <structfield>typtype</structfield>), then this column points to
       the <link linkend="catalog-pg-class"><structname>pg_class</structname></link> entry that defines the
       corresponding table.  (For a free-standing composite type, the
       <link linkend="catalog-pg-class"><structname>pg_class</structname></link> entry doesn't really represent
       a table, but it is needed anyway for the type's
       <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link> entries to link to.)
       Zero for non-composite types.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typsubscript</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Subscripting handler function's OID, or zero if this type doesn't
       support subscripting.  Types that are <quote>true</quote> array
       types have <structfield>typsubscript</structfield>
       = <function>array_subscript_handler</function>, but other types may
       have other handler functions to implement specialized subscripting
       behavior.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typelem</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If <structfield>typelem</structfield> is not zero then it
       identifies another row in <structname>pg_type</structname>,
       defining the type yielded by subscripting.  This should be zero
       if <structfield>typsubscript</structfield> is zero.  However, it can
       be zero when <structfield>typsubscript</structfield> isn't zero, if the
       handler doesn't need <structfield>typelem</structfield> to
       determine the subscripting result type.
       Note that a <structfield>typelem</structfield> dependency is
       considered to imply physical containment of the element type in
       this type; so DDL changes on the element type might be restricted
       by the presence of this type.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typarray</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If <structfield>typarray</structfield> is not zero then it
       identifies another row in <structname>pg_type</structname>, which
       is the <quote>true</quote> array type having this type as element
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typinput</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Input conversion function (text format)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typoutput</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Output conversion function (text format)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typreceive</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Input conversion function (binary format), or zero if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typsend</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Output conversion function (binary format), or zero if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typmodin</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Type modifier input function, or zero if type does not support modifiers
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typmodout</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Type modifier output function, or zero to use the standard format
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typanalyze</structfield> <type>regproc</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Custom <xref linkend="sql-analyze"/> function,
       or zero to use the standard function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typalign</structfield> <type>char</type>
      </para>
      <para>
       <structfield>typalign</structfield> is the alignment required
       when storing a value of this type.  It applies to storage on
       disk as well as most representations of the value inside
       <productname>PostgreSQL</productname>.
       When multiple values are stored consecutively, such
       as in the representation of a complete row on disk, padding is
       inserted before a datum of this type so that it begins on the
       specified boundary.  The alignment reference is the beginning
       of the first datum in the sequence.
       Possible values are:
       <itemizedlist>
        <listitem>
         <para><literal>c</literal> = <type>char</type> alignment, i.e., no alignment needed.</para>
        </listitem>
        <listitem>
         <para><literal>s</literal> = <type>short</type> alignment (2 bytes on most machines).</para>
        </listitem>
        <listitem>
         <para><literal>i</literal> = <type>int</type> alignment (4 bytes on most machines).</para>
        </listitem>
        <listitem>
         <para><literal>d</literal> = <type>double</type> alignment (8 bytes on many machines, but by no means all).</para>
        </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typstorage</structfield> <type>char</type>
      </para>
      <para>
       <structfield>typstorage</structfield> tells for varlena
       types (those with <structfield>typlen</structfield> = -1) if
       the type is prepared for toasting and what the default strategy
       for attributes of this type should be.
       Possible values are:
       <itemizedlist>
        <listitem>
         <para>
          <literal>p</literal> (plain): Values must always be stored plain
          (non-varlena types always use this value).
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>e</literal> (external): Values can be stored in a
          secondary <quote>TOAST</quote> relation (if relation has one, see
          <literal>pg_class.reltoastrelid</literal>).
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>m</literal> (main): Values can be compressed and stored
          inline.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>x</literal> (extended): Values can be compressed and/or
          moved to a secondary relation.
         </para>
        </listitem>
       </itemizedlist>
       <literal>x</literal> is the usual choice for toast-able types.
       Note that <literal>m</literal> values can also be moved out to
       secondary storage, but only as a last resort (<literal>e</literal>
       and <literal>x</literal> values are moved first).
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typnotnull</structfield> <type>bool</type>
      </para>
      <para>
       <structfield>typnotnull</structfield> represents a not-null
       constraint on a type.  Used for domains only.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typbasetype</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       If this is a domain (see <structfield>typtype</structfield>), then
       <structfield>typbasetype</structfield> identifies the type that this
       one is based on.  Zero if this type is not a domain.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typtypmod</structfield> <type>int4</type>
      </para>
      <para>
       Domains use <structfield>typtypmod</structfield> to record the <literal>typmod</literal>
       to be applied to their base type (-1 if base type does not use a
       <literal>typmod</literal>).  -1 if this type is not a domain.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typndims</structfield> <type>int4</type>
      </para>
      <para>
       <structfield>typndims</structfield> is the number of array dimensions
       for a domain over an array (that is, <structfield>typbasetype</structfield> is
       an array type).
       Zero for types other than domains over array types.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typcollation</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-collation"><structname>pg_collation</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       <structfield>typcollation</structfield> specifies the collation
       of the type.  If the type does not support collations, this will
       be zero.  A base type that supports collations will have a nonzero
       value here, typically <symbol>DEFAULT_COLLATION_OID</symbol>.
       A domain over a collatable type can have a collation OID different
       from its base type's, if one was specified for the domain.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typdefaultbin</structfield> <type>pg_node_tree</type>
      </para>
      <para>
       If <structfield>typdefaultbin</structfield> is not null, it is the
       <function>nodeToString()</function>
       representation of a default expression for the type.  This is
       only used for domains.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typdefault</structfield> <type>text</type>
      </para>
      <para>
       <structfield>typdefault</structfield> is null if the type has no associated
       default value. If <structfield>typdefaultbin</structfield> is not null,
       <structfield>typdefault</structfield> must contain a human-readable version of the
       default expression represented by <structfield>typdefaultbin</structfield>.  If
       <structfield>typdefaultbin</structfield> is null and <structfield>typdefault</structfield> is
       not, then <structfield>typdefault</structfield> is the external representation of
       the type's default value, which can be fed to the type's input
       converter to produce a constant.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>typacl</structfield> <type>aclitem[]</type>
      </para>
      <para>
       Access privileges; see <xref linkend="ddl-priv"/> for details
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <note>
   <para>
    For fixed-width types used in system tables, it is critical that the size
    and alignment defined in <structname>pg_type</structname>
    agree with the way that the compiler will lay out the column in
    a structure representing a table row.
   </para>
  </note>

  <para>
   <xref linkend="catalog-typcategory-table"/> lists the system-defined values
   of <structfield>typcategory</structfield>.  Any future additions to this list will
   also be upper-case ASCII letters.  All other ASCII characters are reserved
   for user-defined categories.
  </para>

  <table id="catalog-typcategory-table">
   <title><structfield>typcategory</structfield> Codes</title>

   <tgroup cols="2">
    <thead>
     <row>
      <entry>Code</entry>
      <entry>Category</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>A</literal></entry>
      <entry>Array types</entry>
     </row>
     <row>
      <entry><literal>B</literal></entry>
      <entry>Boolean types</entry>
     </row>
     <row>
      <entry><literal>C</literal></entry>
      <entry>Composite types</entry>
     </row>
     <row>
      <entry><literal>D</literal></entry>
      <entry>Date/time types</entry>
     </row>
     <row>
      <entry><literal>E</literal></entry>
      <entry>Enum types</entry>
     </row>
     <row>
      <entry><literal>G</literal></entry>
      <entry>Geometric types</entry>
     </row>
     <row>
      <entry><literal>I</literal></entry>
      <entry>Network address types</entry>
     </row>
     <row>
      <entry><literal>N</literal></entry>
      <entry>Numeric types</entry>
     </row>
     <row>
      <entry><literal>P</literal></entry>
      <entry>Pseudo-types</entry>
     </row>
     <row>
      <entry><literal>R</literal></entry>
      <entry>Range types</entry>
     </row>
     <row>
      <entry><literal>S</literal></entry>
      <entry>String types</entry>
     </row>
     <row>
      <entry><literal>T</literal></entry>
      <entry>Timespan types</entry>
     </row>
     <row>
      <entry><literal>U</literal></entry>
      <entry>User-defined types</entry>
     </row>
     <row>
      <entry><literal>V</literal></entry>
      <entry>Bit-string types</entry>
     </row>
     <row>
      <entry><literal>X</literal></entry>
      <entry><type>unknown</type> type</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-user-mapping">
  <title><structname>pg_user_mapping</structname></title>

  <indexterm zone="catalog-pg-user-mapping">
   <primary>pg_user_mapping</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_user_mapping</structname> stores
   the mappings from local user to remote.  Access to this catalog is
   restricted from normal users, use the view
   <link linkend="view-pg-user-mappings"><structname>pg_user_mappings</structname></link>
   instead.
  </para>

  <table>
   <title><structname>pg_user_mapping</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>umuser</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the local role being mapped, or zero if the user mapping is public
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>umserver</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-foreign-server"><structname>pg_foreign_server</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the foreign server that contains this mapping
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>umoptions</structfield> <type>text[]</type>
      </para>
      <para>
       User mapping specific options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>


 <sect1 id="views-overview">
  <title>System Views</title>

  <para>
   In addition to the system catalogs, <productname>PostgreSQL</productname>
   provides a number of built-in views.  Some system views provide convenient
   access to some commonly used queries on the system catalogs.  Other views
   provide access to internal server state.
  </para>

  <para>
   The information schema (<xref linkend="information-schema"/>) provides
   an alternative set of views which overlap the functionality of the system
   views.  Since the information schema is SQL-standard whereas the views
   described here are <productname>PostgreSQL</productname>-specific,
   it's usually better to use the information schema if it provides all
   the information you need.
  </para>

  <para>
   <xref linkend="view-table"/> lists the system views described here.
   More detailed documentation of each view follows below.
   There are some additional views that provide access to the results of
   the statistics collector; they are described in <xref
   linkend="monitoring-stats-views-table"/>.
  </para>

  <para>
   Except where noted, all the views described here are read-only.
  </para>

  <table id="view-table">
   <title>System Views</title>

   <tgroup cols="2">
    <thead>
     <row>
      <entry>View Name</entry>
      <entry>Purpose</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><link linkend="view-pg-available-extensions"><structname>pg_available_extensions</structname></link></entry>
      <entry>available extensions</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-available-extension-versions"><structname>pg_available_extension_versions</structname></link></entry>
      <entry>available versions of extensions</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-backend-memory-contexts"><structname>pg_backend_memory_contexts</structname></link></entry>
      <entry>backend memory contexts</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-config"><structname>pg_config</structname></link></entry>
      <entry>compile-time configuration parameters</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-cursors"><structname>pg_cursors</structname></link></entry>
      <entry>open cursors</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-file-settings"><structname>pg_file_settings</structname></link></entry>
      <entry>summary of configuration file contents</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-group"><structname>pg_group</structname></link></entry>
      <entry>groups of database users</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-hba-file-rules"><structname>pg_hba_file_rules</structname></link></entry>
      <entry>summary of client authentication configuration file contents</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-indexes"><structname>pg_indexes</structname></link></entry>
      <entry>indexes</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-locks"><structname>pg_locks</structname></link></entry>
      <entry>locks currently held or awaited</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-matviews"><structname>pg_matviews</structname></link></entry>
      <entry>materialized views</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-policies"><structname>pg_policies</structname></link></entry>
      <entry>policies</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-prepared-statements"><structname>pg_prepared_statements</structname></link></entry>
      <entry>prepared statements</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link></entry>
      <entry>prepared transactions</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-publication-tables"><structname>pg_publication_tables</structname></link></entry>
      <entry>publications and their associated tables</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-replication-origin-status"><structname>pg_replication_origin_status</structname></link></entry>
      <entry>information about replication origins, including replication progress</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-replication-slots"><structname>pg_replication_slots</structname></link></entry>
      <entry>replication slot information</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-roles"><structname>pg_roles</structname></link></entry>
      <entry>database roles</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-rules"><structname>pg_rules</structname></link></entry>
      <entry>rules</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-seclabels"><structname>pg_seclabels</structname></link></entry>
      <entry>security labels</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-sequences"><structname>pg_sequences</structname></link></entry>
      <entry>sequences</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-settings"><structname>pg_settings</structname></link></entry>
      <entry>parameter settings</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-shadow"><structname>pg_shadow</structname></link></entry>
      <entry>database users</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-shmem-allocations"><structname>pg_shmem_allocations</structname></link></entry>
      <entry>shared memory allocations</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-stats"><structname>pg_stats</structname></link></entry>
      <entry>planner statistics</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-stats-ext"><structname>pg_stats_ext</structname></link></entry>
      <entry>extended planner statistics</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-stats-ext-exprs"><structname>pg_stats_ext_exprs</structname></link></entry>
      <entry>extended planner statistics for expressions</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-tables"><structname>pg_tables</structname></link></entry>
      <entry>tables</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-timezone-abbrevs"><structname>pg_timezone_abbrevs</structname></link></entry>
      <entry>time zone abbreviations</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-timezone-names"><structname>pg_timezone_names</structname></link></entry>
      <entry>time zone names</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-user"><structname>pg_user</structname></link></entry>
      <entry>database users</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-user-mappings"><structname>pg_user_mappings</structname></link></entry>
      <entry>user mappings</entry>
     </row>

     <row>
      <entry><link linkend="view-pg-views"><structname>pg_views</structname></link></entry>
      <entry>views</entry>
     </row>

    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="view-pg-available-extensions">
  <title><structname>pg_available_extensions</structname></title>

  <indexterm zone="view-pg-available-extensions">
   <primary>pg_available_extensions</primary>
  </indexterm>

  <para>
   The <structname>pg_available_extensions</structname> view lists the
   extensions that are available for installation.
   See also the
   <link linkend="catalog-pg-extension"><structname>pg_extension</structname></link>
   catalog, which shows the extensions currently installed.
  </para>

  <table>
   <title><structname>pg_available_extensions</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>name</type>
      </para>
      <para>
       Extension name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>default_version</structfield> <type>text</type>
      </para>
      <para>
       Name of default version, or <literal>NULL</literal> if none is
       specified
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>installed_version</structfield> <type>text</type>
      </para>
      <para>
       Currently installed version of the extension,
       or <literal>NULL</literal> if not installed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>comment</structfield> <type>text</type>
      </para>
      <para>
       Comment string from the extension's control file
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The <structname>pg_available_extensions</structname> view is read-only.
  </para>
 </sect1>

 <sect1 id="view-pg-available-extension-versions">
  <title><structname>pg_available_extension_versions</structname></title>

  <indexterm zone="view-pg-available-extension-versions">
   <primary>pg_available_extension_versions</primary>
  </indexterm>

  <para>
   The <structname>pg_available_extension_versions</structname> view lists the
   specific extension versions that are available for installation.
   See also the <link
   linkend="catalog-pg-extension"><structname>pg_extension</structname></link>
   catalog, which shows the extensions currently installed.
  </para>

  <table>
   <title><structname>pg_available_extension_versions</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>name</type>
      </para>
      <para>
       Extension name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>version</structfield> <type>text</type>
      </para>
      <para>
       Version name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>installed</structfield> <type>bool</type>
      </para>
      <para>
       True if this version of this extension is currently
       installed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>superuser</structfield> <type>bool</type>
      </para>
      <para>
       True if only superusers are allowed to install this extension
       (but see <structfield>trusted</structfield>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>trusted</structfield> <type>bool</type>
      </para>
      <para>
       True if the extension can be installed by non-superusers
       with appropriate privileges
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relocatable</structfield> <type>bool</type>
      </para>
      <para>
       True if extension can be relocated to another schema
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schema</structfield> <type>name</type>
      </para>
      <para>
       Name of the schema that the extension must be installed into,
       or <literal>NULL</literal> if partially or fully relocatable
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>requires</structfield> <type>name[]</type>
      </para>
      <para>
       Names of prerequisite extensions,
       or <literal>NULL</literal> if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>comment</structfield> <type>text</type>
      </para>
      <para>
       Comment string from the extension's control file
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The <structname>pg_available_extension_versions</structname> view is
   read-only.
  </para>
 </sect1>

 <sect1 id="view-pg-backend-memory-contexts">
  <title><structname>pg_backend_memory_contexts</structname></title>

  <indexterm zone="view-pg-backend-memory-contexts">
   <primary>pg_backend_memory_contexts</primary>
  </indexterm>

  <para>
   The view <structname>pg_backend_memory_contexts</structname> displays all
   the memory contexts of the server process attached to the current session.
  </para>
  <para>
   <structname>pg_backend_memory_contexts</structname> contains one row
   for each memory context.
  </para>

  <table>
   <title><structname>pg_backend_memory_contexts</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       Name of the memory context
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ident</structfield> <type>text</type>
      </para>
      <para>
       Identification information of the memory context. This field is truncated at 1024 bytes
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>parent</structfield> <type>text</type>
      </para>
      <para>
       Name of the parent of this memory context
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>level</structfield> <type>int4</type>
      </para>
      <para>
       Distance from TopMemoryContext in context tree
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>total_bytes</structfield> <type>int8</type>
      </para>
      <para>
       Total bytes allocated for this memory context
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>total_nblocks</structfield> <type>int8</type>
      </para>
      <para>
       Total number of blocks allocated for this memory context
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>free_bytes</structfield> <type>int8</type>
      </para>
      <para>
       Free space in bytes
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>free_chunks</structfield> <type>int8</type>
      </para>
      <para>
       Total number of free chunks
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>used_bytes</structfield> <type>int8</type>
      </para>
      <para>
       Used space in bytes
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   By default, the <structname>pg_backend_memory_contexts</structname> view can be
   read only by superusers.
  </para>
 </sect1>

 <sect1 id="view-pg-config">
  <title><structname>pg_config</structname></title>

  <indexterm zone="view-pg-config">
   <primary>pg_config</primary>
  </indexterm>

  <para>
   The view <structname>pg_config</structname> describes the
   compile-time configuration parameters of the currently installed
   version of <productname>PostgreSQL</productname>. It is intended, for example, to
   be used by software packages that want to interface to
   <productname>PostgreSQL</productname> to facilitate finding the required header
   files and libraries. It provides the same basic information as the
   <xref linkend="app-pgconfig"/> <productname>PostgreSQL</productname> client
   application.
  </para>

  <para>
   By default, the <structname>pg_config</structname> view can be read
   only by superusers.
  </para>

  <table>
   <title><structname>pg_config</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       The parameter name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>setting</structfield> <type>text</type>
      </para>
      <para>
       The parameter value
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-cursors">
  <title><structname>pg_cursors</structname></title>

  <indexterm zone="view-pg-cursors">
   <primary>pg_cursors</primary>
  </indexterm>

  <para>
   The <structname>pg_cursors</structname> view lists the cursors that
   are currently available. Cursors can be defined in several ways:
   <itemizedlist>
    <listitem>
     <para>
      via the <link linkend="sql-declare"><command>DECLARE</command></link>
      statement in SQL
     </para>
    </listitem>

    <listitem>
     <para>
      via the Bind message in the frontend/backend protocol, as
      described in <xref linkend="protocol-flow-ext-query"/>
     </para>
    </listitem>

    <listitem>
     <para>
      via the Server Programming Interface (SPI), as described in
      <xref linkend="spi-interface"/>
     </para>
    </listitem>
   </itemizedlist>

   The <structname>pg_cursors</structname> view displays cursors
   created by any of these means. Cursors only exist for the duration
   of the transaction that defines them, unless they have been
   declared <literal>WITH HOLD</literal>. Therefore non-holdable
   cursors are only present in the view until the end of their
   creating transaction.

   <note>
    <para>
     Cursors are used internally to implement some of the components
     of <productname>PostgreSQL</productname>, such as procedural languages.
     Therefore, the <structname>pg_cursors</structname> view might include cursors
     that have not been explicitly created by the user.
    </para>
   </note>
  </para>

  <table>
   <title><structname>pg_cursors</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       The name of the cursor
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>statement</structfield> <type>text</type>
      </para>
      <para>
       The verbatim query string submitted to declare this cursor
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>is_holdable</structfield> <type>bool</type>
      </para>
      <para>
       <literal>true</literal> if the cursor is holdable (that is, it
       can be accessed after the transaction that declared the cursor
       has committed); <literal>false</literal> otherwise
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>is_binary</structfield> <type>bool</type>
      </para>
      <para>
       <literal>true</literal> if the cursor was declared
       <literal>BINARY</literal>; <literal>false</literal>
       otherwise
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>is_scrollable</structfield> <type>bool</type>
      </para>
      <para>
       <literal>true</literal> if the cursor is scrollable (that is, it
       allows rows to be retrieved in a nonsequential manner);
       <literal>false</literal> otherwise
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>creation_time</structfield> <type>timestamptz</type>
      </para>
      <para>
       The time at which the cursor was declared
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The <structname>pg_cursors</structname> view is read-only.
  </para>

 </sect1>

 <sect1 id="view-pg-file-settings">
  <title><structname>pg_file_settings</structname></title>

  <indexterm zone="view-pg-file-settings">
   <primary>pg_file_settings</primary>
  </indexterm>

  <para>
   The view <structname>pg_file_settings</structname> provides a summary of
   the contents of the server's configuration file(s).  A row appears in
   this view for each <quote>name = value</quote> entry appearing in the files,
   with annotations indicating whether the value could be applied
   successfully.  Additional row(s) may appear for problems not linked to
   a <quote>name = value</quote> entry, such as syntax errors in the files.
  </para>

  <para>
   This view is helpful for checking whether planned changes in the
   configuration files will work, or for diagnosing a previous failure.
   Note that this view reports on the <emphasis>current</emphasis> contents of the
   files, not on what was last applied by the server.  (The
   <link linkend="view-pg-settings"><structname>pg_settings</structname></link>
   view is usually sufficient to determine that.)
  </para>

  <para>
   By default, the <structname>pg_file_settings</structname> view can be read
   only by superusers.
  </para>

  <table>
   <title><structname>pg_file_settings</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sourcefile</structfield> <type>text</type>
      </para>
      <para>
       Full path name of the configuration file
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sourceline</structfield> <type>int4</type>
      </para>
      <para>
       Line number within the configuration file where the entry appears
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seqno</structfield> <type>int4</type>
      </para>
      <para>
       Order in which the entries are processed (1..<replaceable>n</replaceable>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       Configuration parameter name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>setting</structfield> <type>text</type>
      </para>
      <para>
       Value to be assigned to the parameter
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>applied</structfield> <type>bool</type>
      </para>
      <para>
       True if the value can be applied successfully
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>error</structfield> <type>text</type>
      </para>
      <para>
       If not null, an error message indicating why this entry could
       not be applied
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   If the configuration file contains syntax errors or invalid parameter
   names, the server will not attempt to apply any settings from it, and
   therefore all the <structfield>applied</structfield> fields will read as false.
   In such a case there will be one or more rows with
   non-null <structfield>error</structfield> fields indicating the
   problem(s).  Otherwise, individual settings will be applied if possible.
   If an individual setting cannot be applied (e.g., invalid value, or the
   setting cannot be changed after server start) it will have an appropriate
   message in the <structfield>error</structfield> field.  Another way that
   an entry might have <structfield>applied</structfield> = false is that it is
   overridden by a later entry for the same parameter name; this case is not
   considered an error so nothing appears in
   the <structfield>error</structfield> field.
  </para>

  <para>
   See <xref linkend="config-setting"/> for more information about the various
   ways to change run-time parameters.
  </para>

</sect1>

 <sect1 id="view-pg-group">
  <title><structname>pg_group</structname></title>

  <indexterm zone="view-pg-group">
   <primary>pg_group</primary>
  </indexterm>

  <!-- Unlike information_schema.applicable_roles, this shows no members for
       pg_database_owner.  The v8.1 catalog would have shown no members if
       that role had existed at the time. -->
  <para>
   The view <structname>pg_group</structname> exists for backwards
   compatibility: it emulates a catalog that existed in
   <productname>PostgreSQL</productname> before version 8.1.
   It shows the names and members of all roles that are marked as not
   <structfield>rolcanlogin</structfield>, which is an approximation to the set
   of roles that are being used as groups.
  </para>

  <table>
   <title><structname>pg_group</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>groname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       Name of the group
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>grosysid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       ID of this group
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>grolist</structfield> <type>oid[]</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       An array containing the IDs of the roles in this group
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-hba-file-rules">
  <title><structname>pg_hba_file_rules</structname></title>

  <indexterm zone="view-pg-hba-file-rules">
   <primary>pg_hba_file_rules</primary>
  </indexterm>

  <para>
   The view <structname>pg_hba_file_rules</structname> provides a summary of
   the contents of the client authentication configuration file,
   <link linkend="auth-pg-hba-conf"><filename>pg_hba.conf</filename></link>.
   A row appears in this view for each
   non-empty, non-comment line in the file, with annotations indicating
   whether the rule could be applied successfully.
  </para>

  <para>
   This view can be helpful for checking whether planned changes in the
   authentication configuration file will work, or for diagnosing a previous
   failure.  Note that this view reports on the <emphasis>current</emphasis> contents
   of the file, not on what was last loaded by the server.
  </para>

  <para>
   By default, the <structname>pg_hba_file_rules</structname> view can be read
   only by superusers.
  </para>

  <table>
   <title><structname>pg_hba_file_rules</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>line_number</structfield> <type>int4</type>
      </para>
      <para>
       Line number of this rule in <filename>pg_hba.conf</filename>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>type</structfield> <type>text</type>
      </para>
      <para>
       Type of connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>database</structfield> <type>text[]</type>
      </para>
      <para>
       List of database name(s) to which this rule applies
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>user_name</structfield> <type>text[]</type>
      </para>
      <para>
       List of user and group name(s) to which this rule applies
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>address</structfield> <type>text</type>
      </para>
      <para>
       Host name or IP address, or one
       of <literal>all</literal>, <literal>samehost</literal>,
       or <literal>samenet</literal>, or null for local connections
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>netmask</structfield> <type>text</type>
      </para>
      <para>
       IP address mask, or null if not applicable
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>auth_method</structfield> <type>text</type>
      </para>
      <para>
       Authentication method
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>options</structfield> <type>text[]</type>
      </para>
      <para>
       Options specified for authentication method, if any
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>error</structfield> <type>text</type>
      </para>
      <para>
       If not null, an error message indicating why this
       line could not be processed
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Usually, a row reflecting an incorrect entry will have values for only
   the <structfield>line_number</structfield> and <structfield>error</structfield> fields.
  </para>

  <para>
   See <xref linkend="client-authentication"/> for more information about
   client authentication configuration.
  </para>
 </sect1>

 <sect1 id="view-pg-indexes">
  <title><structname>pg_indexes</structname></title>

  <indexterm zone="view-pg-indexes">
   <primary>pg_indexes</primary>
  </indexterm>

  <para>
   The view <structname>pg_indexes</structname> provides access to
   useful information about each index in the database.
  </para>

  <table>
   <title><structname>pg_indexes</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing table and index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of table the index is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indexname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablespace</structfield> <type>name</type>
       (references <link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.<structfield>spcname</structfield>)
      </para>
      <para>
       Name of tablespace containing index (null if default for database)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indexdef</structfield> <type>text</type>
      </para>
      <para>
       Index definition (a reconstructed <xref linkend="sql-createindex"/>
       command)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-locks">
  <title><structname>pg_locks</structname></title>

  <indexterm zone="view-pg-locks">
   <primary>pg_locks</primary>
  </indexterm>

  <para>
   The view <structname>pg_locks</structname> provides access to
   information about the locks held by active processes within the
   database server.  See <xref linkend="mvcc"/> for more discussion
   of locking.
  </para>

  <para>
   <structname>pg_locks</structname> contains one row per active lockable
   object, requested lock mode, and relevant process.  Thus, the same
   lockable object might
   appear many times, if multiple processes are holding or waiting
   for locks on it.  However, an object that currently has no locks on it
   will not appear at all.
  </para>

  <para>
   There are several distinct types of lockable objects:
   whole relations (e.g., tables), individual pages of relations,
   individual tuples of relations,
   transaction IDs (both virtual and permanent IDs),
   and general database objects (identified by class OID and object OID,
   in the same way as in <link linkend="catalog-pg-description"><structname>pg_description</structname></link> or
   <link linkend="catalog-pg-depend"><structname>pg_depend</structname></link>).  Also, the right to extend a
   relation is represented as a separate lockable object, as is the right to
   update <structname>pg_database</structname>.<structfield>datfrozenxid</structfield>.
   Also, <quote>advisory</quote> locks can be taken on numbers that have
   user-defined meanings.
  </para>

  <table>
   <title><structname>pg_locks</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>locktype</structfield> <type>text</type>
      </para>
      <para>
       Type of the lockable object:
       <literal>relation</literal>,
       <literal>extend</literal>,
       <literal>frozenid</literal>,
       <literal>page</literal>,
       <literal>tuple</literal>,
       <literal>transactionid</literal>,
       <literal>virtualxid</literal>,
       <literal>spectoken</literal>,
       <literal>object</literal>,
       <literal>userlock</literal>, or
       <literal>advisory</literal>.
       (See also <xref linkend="wait-event-lock-table"/>.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>database</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-database"><structname>pg_database</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the database in which the lock target exists, or
       zero if the target is a shared object, or
       null if the target is a transaction ID
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relation</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the relation targeted by the lock, or null if the target is not
       a relation or part of a relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>page</structfield> <type>int4</type>
      </para>
      <para>
       Page number targeted by the lock within the relation,
       or null if the target is not a relation page or tuple
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tuple</structfield> <type>int2</type>
      </para>
      <para>
       Tuple number targeted by the lock within the page,
       or null if the target is not a tuple
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>virtualxid</structfield> <type>text</type>
      </para>
      <para>
       Virtual ID of the transaction targeted by the lock,
       or null if the target is not a virtual transaction ID
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>transactionid</structfield> <type>xid</type>
      </para>
      <para>
       ID of the transaction targeted by the lock,
       or null if the target is not a transaction ID
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the system catalog containing the lock target, or null if the
       target is not a general database object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       OID of the lock target within its system catalog, or null if the
       target is not a general database object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objsubid</structfield> <type>int2</type>
      </para>
      <para>
       Column number targeted by the lock (the
       <structfield>classid</structfield> and <structfield>objid</structfield> refer to the
       table itself),
       or zero if the target is some other general database object,
       or null if the target is not a general database object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>virtualtransaction</structfield> <type>text</type>
      </para>
      <para>
       Virtual ID of the transaction that is holding or awaiting this lock
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>int4</type>
      </para>
      <para>
       Process ID of the server process holding or awaiting this
       lock, or null if the lock is held by a prepared transaction
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>mode</structfield> <type>text</type>
      </para>
      <para>
       Name of the lock mode held or desired by this process (see <xref linkend="locking-tables"/> and <xref linkend="xact-serializable"/>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>granted</structfield> <type>bool</type>
      </para>
      <para>
       True if lock is held, false if lock is awaited
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fastpath</structfield> <type>bool</type>
      </para>
      <para>
       True if lock was taken via fast path, false if taken via main
       lock table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>waitstart</structfield> <type>timestamptz</type>
      </para>
      <para>
       Time when the server process started waiting for this lock,
       or null if the lock is held.
       Note that this can be null for a very short period of time after
       the wait started even though <structfield>granted</structfield>
       is <literal>false</literal>.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   <structfield>granted</structfield> is true in a row representing a lock
   held by the indicated process.  False indicates that this process is
   currently waiting to acquire this lock, which implies that at least one
   other process is holding or waiting for a conflicting lock mode on the same
   lockable object.  The waiting process will sleep until the other lock is
   released (or a deadlock situation is detected).  A single process can be
   waiting to acquire at most one lock at a time.
  </para>

  <para>
   Throughout running a transaction, a server process holds an exclusive lock
   on the transaction's virtual transaction ID.  If a permanent ID is assigned
   to the transaction (which normally happens only if the transaction changes
   the state of the database), it also holds an exclusive lock on the
   transaction's permanent transaction ID until it ends.  When a process finds
   it necessary to wait specifically for another transaction to end, it does
   so by attempting to acquire share lock on the other transaction's ID
   (either virtual or permanent ID depending on the situation). That will
   succeed only when the other transaction terminates and releases its locks.
  </para>

  <para>
   Although tuples are a lockable type of object,
   information about row-level locks is stored on disk, not in memory,
   and therefore row-level locks normally do not appear in this view.
   If a process is waiting for a
   row-level lock, it will usually appear in the view as waiting for the
   permanent transaction ID of the current holder of that row lock.
  </para>

  <para>
   Advisory locks can be acquired on keys consisting of either a single
   <type>bigint</type> value or two integer values.
   A <type>bigint</type> key is displayed with its
   high-order half in the <structfield>classid</structfield> column, its low-order half
   in the <structfield>objid</structfield> column, and <structfield>objsubid</structfield> equal
   to 1. The original <type>bigint</type> value can be reassembled with the
   expression <literal>(classid::bigint &lt;&lt; 32) |
   objid::bigint</literal>. Integer keys are displayed with the
   first key in the
   <structfield>classid</structfield> column, the second key in the <structfield>objid</structfield>
   column, and <structfield>objsubid</structfield> equal to 2.  The actual meaning of
   the keys is up to the user.  Advisory locks are local to each database,
   so the <structfield>database</structfield> column is meaningful for an advisory lock.
  </para>

  <para>
   <structname>pg_locks</structname> provides a global view of all locks
   in the database cluster, not only those relevant to the current database.
   Although its <structfield>relation</structfield> column can be joined
   against <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield> to identify locked
   relations, this will only work correctly for relations in the current
   database (those for which the <structfield>database</structfield> column
   is either the current database's OID or zero).
  </para>

  <para>
   The <structfield>pid</structfield> column can be joined to the
   <structfield>pid</structfield> column of the
   <link linkend="monitoring-pg-stat-activity-view">
   <structname>pg_stat_activity</structname></link>
   view to get more
   information on the session holding or awaiting each lock,
   for example
<programlisting>
SELECT * FROM pg_locks pl LEFT JOIN pg_stat_activity psa
    ON pl.pid = psa.pid;
</programlisting>
   Also, if you are using prepared transactions, the
   <structfield>virtualtransaction</structfield> column can be joined to the
   <structfield>transaction</structfield> column of the <link
   linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link>
   view to get more information on prepared transactions that hold locks.
   (A prepared transaction can never be waiting for a lock,
   but it continues to hold the locks it acquired while running.)
   For example:
<programlisting>
SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
    ON pl.virtualtransaction = '-1/' || ppx.transaction;
</programlisting>
  </para>

  <para>
   While it is possible to obtain information about which processes block
   which other processes by joining <structname>pg_locks</structname> against
   itself, this is very difficult to get right in detail.  Such a query would
   have to encode knowledge about which lock modes conflict with which
   others.  Worse, the <structname>pg_locks</structname> view does not expose
   information about which processes are ahead of which others in lock wait
   queues, nor information about which processes are parallel workers running
   on behalf of which other client sessions.  It is better to use
   the <function>pg_blocking_pids()</function> function
   (see <xref linkend="functions-info-session-table"/>) to identify which
   process(es) a waiting process is blocked behind.
  </para>

  <para>
   The <structname>pg_locks</structname> view displays data from both the
   regular lock manager and the predicate lock manager, which are
   separate systems; in addition, the regular lock manager subdivides its
   locks into regular and <firstterm>fast-path</firstterm> locks.
   This data is not guaranteed to be entirely consistent.
   When the view is queried,
   data on fast-path locks (with <structfield>fastpath</structfield> = <literal>true</literal>)
   is gathered from each backend one at a time, without freezing the state of
   the entire lock manager, so it is possible for locks to be taken or
   released while information is gathered.  Note, however, that these locks are
   known not to conflict with any other lock currently in place.  After
   all backends have been queried for fast-path locks, the remainder of the
   regular lock manager is locked as a unit, and a consistent snapshot of all
   remaining locks is collected as an atomic action.  After unlocking the
   regular lock manager, the predicate lock manager is similarly locked and all
   predicate locks are collected as an atomic action.  Thus, with the exception
   of fast-path locks, each lock manager will deliver a consistent set of
   results, but as we do not lock both lock managers simultaneously, it is
   possible for locks to be taken or released after we interrogate the regular
   lock manager and before we interrogate the predicate lock manager.
  </para>

  <para>
   Locking the regular and/or predicate lock manager could have some
   impact on database performance if this view is very frequently accessed.
   The locks are held only for the minimum amount of time necessary to
   obtain data from the lock managers, but this does not completely eliminate
   the possibility of a performance impact.
  </para>

 </sect1>

 <sect1 id="view-pg-matviews">
  <title><structname>pg_matviews</structname></title>

  <indexterm zone="view-pg-matviews">
   <primary>pg_matviews</primary>
  </indexterm>

  <indexterm zone="view-pg-matviews">
   <primary>materialized views</primary>
  </indexterm>

  <para>
   The view <structname>pg_matviews</structname> provides access to
   useful information about each materialized view in the database.
  </para>

  <table>
   <title><structname>pg_matviews</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing materialized view
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>matviewname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of materialized view
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>matviewowner</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       Name of materialized view's owner
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablespace</structfield> <type>name</type>
       (references <link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.<structfield>spcname</structfield>)
      </para>
      <para>
       Name of tablespace containing materialized view (null if default for database)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>hasindexes</structfield> <type>bool</type>
      </para>
      <para>
       True if materialized view has (or recently had) any indexes
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ispopulated</structfield> <type>bool</type>
      </para>
      <para>
       True if materialized view is currently populated
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>definition</structfield> <type>text</type>
      </para>
      <para>
       Materialized view definition (a reconstructed <xref linkend="sql-select"/> query)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-policies">
  <title><structname>pg_policies</structname></title>

  <indexterm zone="view-pg-policies">
   <primary>pg_policies</primary>
  </indexterm>

  <para>
   The view <structname>pg_policies</structname> provides access to
   useful information about each row-level security policy in the database.
  </para>

  <table>
   <title><structname>pg_policies</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing table policy is on
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of table policy is on
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>policyname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-policy"><structname>pg_policy</structname></link>.<structfield>polname</structfield>)
      </para>
      <para>
       Name of policy
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>permissive</structfield> <type>text</type>
      </para>
      <para>
       Is the policy permissive or restrictive?
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>roles</structfield> <type>name[]</type>
      </para>
      <para>
       The roles to which this policy applies
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cmd</structfield> <type>text</type>
      </para>
      <para>
       The command type to which the policy is applied
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>qual</structfield> <type>text</type>
      </para>
      <para>
       The expression added to the security barrier qualifications for
       queries that this policy applies to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>with_check</structfield> <type>text</type>
      </para>
      <para>
       The expression added to the WITH CHECK qualifications for
       queries that attempt to add rows to this table
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-prepared-statements">
  <title><structname>pg_prepared_statements</structname></title>

  <indexterm zone="view-pg-prepared-statements">
   <primary>pg_prepared_statements</primary>
  </indexterm>

  <para>
   The <structname>pg_prepared_statements</structname> view displays
   all the prepared statements that are available in the current
   session. See <xref linkend="sql-prepare"/> for more information about prepared
   statements.
  </para>

  <para>
   <structname>pg_prepared_statements</structname> contains one row
   for each prepared statement. Rows are added to the view when a new
   prepared statement is created and removed when a prepared statement
   is released (for example, via the <link linkend="sql-deallocate"><command>DEALLOCATE</command></link> command).
  </para>

  <table>
   <title><structname>pg_prepared_statements</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       The identifier of the prepared statement
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>statement</structfield> <type>text</type>
      </para>
      <para>
       The query string submitted by the client to create this
       prepared statement. For prepared statements created via SQL,
       this is the <command>PREPARE</command> statement submitted by
       the client. For prepared statements created via the
       frontend/backend protocol, this is the text of the prepared
       statement itself.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prepare_time</structfield> <type>timestamptz</type>
      </para>
      <para>
       The time at which the prepared statement was created
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>parameter_types</structfield> <type>regtype[]</type>
      </para>
      <para>
       The expected parameter types for the prepared statement in the
       form of an array of <type>regtype</type>. The OID corresponding
       to an element of this array can be obtained by casting the
       <type>regtype</type> value to <type>oid</type>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>from_sql</structfield> <type>bool</type>
      </para>
      <para>
       <literal>true</literal> if the prepared statement was created
       via the <command>PREPARE</command> SQL command;
       <literal>false</literal> if the statement was prepared via the
       frontend/backend protocol
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>generic_plans</structfield> <type>int8</type>
      </para>
      <para>
       Number of times generic plan was chosen
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>custom_plans</structfield> <type>int8</type>
      </para>
      <para>
       Number of times custom plan was chosen
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The <structname>pg_prepared_statements</structname> view is read-only.
  </para>
 </sect1>

 <sect1 id="view-pg-prepared-xacts">
  <title><structname>pg_prepared_xacts</structname></title>

  <indexterm zone="view-pg-prepared-xacts">
   <primary>pg_prepared_xacts</primary>
  </indexterm>

  <para>
   The view <structname>pg_prepared_xacts</structname> displays
   information about transactions that are currently prepared for two-phase
   commit (see <xref linkend="sql-prepare-transaction"/> for details).
  </para>

  <para>
   <structname>pg_prepared_xacts</structname> contains one row per prepared
   transaction.  An entry is removed when the transaction is committed or
   rolled back.
  </para>

  <table>
   <title><structname>pg_prepared_xacts</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>transaction</structfield> <type>xid</type>
      </para>
      <para>
       Numeric transaction identifier of the prepared transaction
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>gid</structfield> <type>text</type>
      </para>
      <para>
       Global transaction identifier that was assigned to the transaction
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>prepared</structfield> <type>timestamptz</type>
      </para>
      <para>
       Time at which the transaction was prepared for commit
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>owner</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       Name of the user that executed the transaction
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>database</structfield> <type>name</type>
       (references <link linkend="catalog-pg-database"><structname>pg_database</structname></link>.<structfield>datname</structfield>)
      </para>
      <para>
       Name of the database in which the transaction was executed
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   When the <structname>pg_prepared_xacts</structname> view is accessed, the
   internal transaction manager data structures are momentarily locked, and
   a copy is made for the view to display.  This ensures that the
   view produces a consistent set of results, while not blocking
   normal operations longer than necessary.  Nonetheless
   there could be some impact on database performance if this view is
   frequently accessed.
  </para>

 </sect1>

 <sect1 id="view-pg-publication-tables">
  <title><structname>pg_publication_tables</structname></title>

  <indexterm zone="view-pg-publication-tables">
   <primary>pg_publication_tables</primary>
  </indexterm>

  <para>
   The view <structname>pg_publication_tables</structname> provides
   information about the mapping between publications and the tables they
   contain.  Unlike the underlying catalog
   <link linkend="catalog-pg-publication-rel"><structname>pg_publication_rel</structname></link>,
   this view expands
   publications defined as <literal>FOR ALL TABLES</literal>, so for such
   publications there will be a row for each eligible table.
  </para>

  <table>
   <title><structname>pg_publication_tables</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pubname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-publication"><structname>pg_publication</structname></link>.<structfield>pubname</structfield>)
      </para>
      <para>
       Name of publication
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of table
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

  <sect1 id="view-pg-replication-origin-status">
  <title><structname>pg_replication_origin_status</structname></title>

  <indexterm zone="view-pg-replication-origin-status">
   <primary>pg_replication_origin_status</primary>
  </indexterm>

  <para>
   The <structname>pg_replication_origin_status</structname> view
   contains information about how far replay for a certain origin has
   progressed.  For more on replication origins
   see <xref linkend="replication-origins"/>.
  </para>

  <table>
   <title><structname>pg_replication_origin_status</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>local_id</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-replication-origin"><structname>pg_replication_origin</structname></link>.<structfield>roident</structfield>)
      </para>
      <para>
       internal node identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>external_id</structfield> <type>text</type>
       (references <link linkend="catalog-pg-replication-origin"><structname>pg_replication_origin</structname></link>.<structfield>roname</structfield>)
      </para>
      <para>
       external node identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>remote_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       The origin node's LSN up to which data has been replicated.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>local_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       This node's LSN at which <literal>remote_lsn</literal> has
       been replicated. Used to flush commit records before persisting
       data to disk when using asynchronous commits.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="view-pg-replication-slots">
  <title><structname>pg_replication_slots</structname></title>

  <indexterm zone="view-pg-replication-slots">
   <primary>pg_replication_slots</primary>
  </indexterm>

  <para>
   The <structname>pg_replication_slots</structname> view provides a listing
   of all replication slots that currently exist on the database cluster,
   along with their current state.
  </para>

  <para>
   For more on replication slots,
   see <xref linkend="streaming-replication-slots"/> and <xref linkend="logicaldecoding"/>.
  </para>

  <table>
   <title><structname>pg_replication_slots</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>slot_name</structfield> <type>name</type>
      </para>
      <para>
       A unique, cluster-wide identifier for the replication slot
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>plugin</structfield> <type>name</type>
      </para>
      <para>
       The base name of the shared object containing the output plugin this logical slot is using, or null for physical slots.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>slot_type</structfield> <type>text</type>
      </para>
      <para>
       The slot type: <literal>physical</literal> or <literal>logical</literal>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-database"><structname>pg_database</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the database this slot is associated with, or
       null. Only logical slots have an associated database.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>database</structfield> <type>name</type>
       (references <link linkend="catalog-pg-database"><structname>pg_database</structname></link>.<structfield>datname</structfield>)
      </para>
      <para>
       The name of the database this slot is associated with, or
       null. Only logical slots have an associated database.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>temporary</structfield> <type>bool</type>
      </para>
      <para>
       True if this is a temporary replication slot. Temporary slots are
       not saved to disk and are automatically dropped on error or when
       the session has finished.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>active</structfield> <type>bool</type>
      </para>
      <para>
       True if this slot is currently actively being used
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>active_pid</structfield> <type>int4</type>
      </para>
      <para>
       The process ID of the session using this slot if the slot
       is currently actively being used. <literal>NULL</literal> if
       inactive.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>xmin</structfield> <type>xid</type>
      </para>
      <para>
       The oldest transaction that this slot needs the database to
       retain.  <literal>VACUUM</literal> cannot remove tuples deleted
       by any later transaction.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>catalog_xmin</structfield> <type>xid</type>
      </para>
      <para>
       The oldest transaction affecting the system catalogs that this
       slot needs the database to retain.  <literal>VACUUM</literal> cannot
       remove catalog tuples deleted by any later transaction.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>restart_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       The address (<literal>LSN</literal>) of oldest WAL which still
       might be required by the consumer of this slot and thus won't be
       automatically removed during checkpoints unless this LSN
       gets behind more than <xref linkend="guc-max-slot-wal-keep-size"/>
       from the current LSN.  <literal>NULL</literal>
       if the <literal>LSN</literal> of this slot has never been reserved.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confirmed_flush_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       The address (<literal>LSN</literal>) up to which the logical
       slot's consumer has confirmed receiving data. Data older than this is
       not available anymore. <literal>NULL</literal> for physical slots.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>wal_status</structfield> <type>text</type>
      </para>
      <para>
       Availability of WAL files claimed by this slot.
       Possible values are:
       <itemizedlist>
        <listitem>
         <para><literal>reserved</literal> means that the claimed files
          are within <varname>max_wal_size</varname>.</para>
        </listitem>
        <listitem>
         <para><literal>extended</literal> means
          that <varname>max_wal_size</varname> is exceeded but the files are
          still retained, either by the replication slot or
          by <varname>wal_keep_size</varname>.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>unreserved</literal> means that the slot no longer
          retains the required WAL files and some of them are to be removed at
          the next checkpoint.  This state can return
          to <literal>reserved</literal> or <literal>extended</literal>.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>lost</literal> means that some required WAL files have
          been removed and this slot is no longer usable.
         </para>
        </listitem>
       </itemizedlist>
       The last two states are seen only when
       <xref linkend="guc-max-slot-wal-keep-size"/> is
       non-negative. If <structfield>restart_lsn</structfield> is NULL, this
       field is null.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>safe_wal_size</structfield> <type>int8</type>
      </para>
      <para>
       The number of bytes that can be written to WAL such that this slot
       is not in danger of getting in state "lost".  It is NULL for lost
       slots, as well as if <varname>max_slot_wal_keep_size</varname>
       is <literal>-1</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>two_phase</structfield> <type>bool</type>
      </para>
      <para>
       True if the slot is enabled for decoding prepared transactions.  Always
       false for physical slots.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="view-pg-roles">
  <title><structname>pg_roles</structname></title>

  <indexterm zone="view-pg-roles">
   <primary>pg_roles</primary>
  </indexterm>

  <para>
   The view <structname>pg_roles</structname> provides access to
   information about database roles.  This is simply a publicly
   readable view of
   <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>
   that blanks out the password field.
  </para>

  <table>
   <title><structname>pg_roles</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolname</structfield> <type>name</type>
      </para>
      <para>
       Role name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolsuper</structfield> <type>bool</type>
      </para>
      <para>
       Role has superuser privileges
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolinherit</structfield> <type>bool</type>
      </para>
      <para>
       Role automatically inherits privileges of roles it is a
       member of
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcreaterole</structfield> <type>bool</type>
      </para>
      <para>
       Role can create more roles
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcreatedb</structfield> <type>bool</type>
      </para>
      <para>
       Role can create databases
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolcanlogin</structfield> <type>bool</type>
      </para>
      <para>
       Role can log in. That is, this role can be given as the initial
       session authorization identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolreplication</structfield> <type>bool</type>
      </para>
      <para>
       Role is a replication role. A replication role can initiate replication
       connections and create and drop replication slots.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolconnlimit</structfield> <type>int4</type>
      </para>
      <para>
       For roles that can log in, this sets maximum number of concurrent
       connections this role can make.  -1 means no limit.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolpassword</structfield> <type>text</type>
      </para>
      <para>
       Not the password (always reads as <literal>********</literal>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolvaliduntil</structfield> <type>timestamptz</type>
      </para>
      <para>
       Password expiry time (only used for password authentication);
       null if no expiration
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolbypassrls</structfield> <type>bool</type>
      </para>
      <para>
       Role bypasses every row-level security policy, see
       <xref linkend="ddl-rowsecurity"/> for more information.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rolconfig</structfield> <type>text[]</type>
      </para>
      <para>
       Role-specific defaults for run-time configuration variables
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       ID of role
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-rules">
  <title><structname>pg_rules</structname></title>

  <indexterm zone="view-pg-rules">
   <primary>pg_rules</primary>
  </indexterm>

  <para>
   The view <structname>pg_rules</structname> provides access to
   useful information about query rewrite rules.
  </para>

  <table>
   <title><structname>pg_rules</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of table the rule is for
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rulename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link>.<structfield>rulename</structfield>)
      </para>
      <para>
       Name of rule
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>definition</structfield> <type>text</type>
      </para>
      <para>
       Rule definition (a reconstructed creation command)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The <structname>pg_rules</structname> view excludes the <literal>ON SELECT</literal> rules
   of views and materialized views; those can be seen in
   <link linkend="view-pg-views"><structname>pg_views</structname></link> and <link linkend="view-pg-matviews"><structname>pg_matviews</structname></link>.
  </para>

 </sect1>

 <sect1 id="view-pg-seclabels">
  <title><structname>pg_seclabels</structname></title>

  <indexterm zone="view-pg-seclabels">
   <primary>pg_seclabels</primary>
  </indexterm>

  <para>
   The view <structname>pg_seclabels</structname> provides information about
   security labels.  It as an easier-to-query version of the
   <link linkend="catalog-pg-seclabel"><structname>pg_seclabel</structname></link> catalog.
  </para>

  <table>
   <title><structname>pg_seclabels</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objoid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the object this security label pertains to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog this object appears in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objsubid</structfield> <type>int4</type>
      </para>
      <para>
       For a security label on a table column, this is the column number (the
       <structfield>objoid</structfield> and <structfield>classoid</structfield> refer to
       the table itself).  For all other object types, this column is
       zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objtype</structfield> <type>text</type>
      </para>
      <para>
       The type of object to which this label applies, as text.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objnamespace</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the namespace for this object, if applicable;
       otherwise NULL.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objname</structfield> <type>text</type>
      </para>
      <para>
       The name of the object to which this label applies, as text.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>provider</structfield> <type>text</type>
       (references <link linkend="catalog-pg-seclabel"><structname>pg_seclabel</structname></link>.<structfield>provider</structfield>)
      </para>
      <para>
       The label provider associated with this label.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>label</structfield> <type>text</type>
       (references <link linkend="catalog-pg-seclabel"><structname>pg_seclabel</structname></link>.<structfield>label</structfield>)
      </para>
      <para>
       The security label applied to this object.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="view-pg-sequences">
  <title><structname>pg_sequences</structname></title>

  <indexterm zone="view-pg-sequences">
   <primary>pg_sequences</primary>
  </indexterm>

  <para>
   The view <structname>pg_sequences</structname> provides access to
   useful information about each sequence in the database.
  </para>

  <table>
   <title><structname>pg_sequences</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sequencename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sequenceowner</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       Name of sequence's owner
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>data_type</structfield> <type>regtype</type>
       (references <link linkend="catalog-pg-type"><structname>pg_type</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Data type of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>start_value</structfield> <type>int8</type>
      </para>
      <para>
       Start value of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>min_value</structfield> <type>int8</type>
      </para>
      <para>
       Minimum value of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>max_value</structfield> <type>int8</type>
      </para>
      <para>
       Maximum value of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>increment_by</structfield> <type>int8</type>
      </para>
      <para>
       Increment value of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cycle</structfield> <type>bool</type>
      </para>
      <para>
       Whether the sequence cycles
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cache_size</structfield> <type>int8</type>
      </para>
      <para>
       Cache size of the sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_value</structfield> <type>int8</type>
      </para>
      <para>
       The last sequence value written to disk.  If caching is used,
       this value can be greater than the last value handed out from the
       sequence.  Null if the sequence has not been read from yet.  Also, if
       the current user does not have <literal>USAGE</literal>
       or <literal>SELECT</literal> privilege on the sequence, the value is
       null.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
 </sect1>

 <sect1 id="view-pg-settings">
  <title><structname>pg_settings</structname></title>

  <indexterm zone="view-pg-settings">
   <primary>pg_settings</primary>
  </indexterm>

  <para>
   The view <structname>pg_settings</structname> provides access to
   run-time parameters of the server.  It is essentially an alternative
   interface to the <link linkend="sql-show"><command>SHOW</command></link>
   and <link linkend="sql-set"><command>SET</command></link> commands.
   It also provides access to some facts about each parameter that are
   not directly available from <link linkend="sql-show"><command>SHOW</command></link>, such as minimum and
   maximum values.
  </para>

  <table>
   <title><structname>pg_settings</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       Run-time configuration parameter name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>setting</structfield> <type>text</type>
      </para>
      <para>
       Current value of the parameter
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>unit</structfield> <type>text</type>
      </para>
      <para>
       Implicit unit of the parameter
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>category</structfield> <type>text</type>
      </para>
      <para>
       Logical group of the parameter
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>short_desc</structfield> <type>text</type>
      </para>
      <para>
       A brief description of the parameter
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extra_desc</structfield> <type>text</type>
      </para>
      <para>
       Additional, more detailed, description of the parameter
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>context</structfield> <type>text</type>
      </para>
      <para>
       Context required to set the parameter's value (see below)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>vartype</structfield> <type>text</type>
      </para>
      <para>
       Parameter type (<literal>bool</literal>, <literal>enum</literal>,
       <literal>integer</literal>, <literal>real</literal>, or <literal>string</literal>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>source</structfield> <type>text</type>
      </para>
      <para>
       Source of the current parameter value
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>min_val</structfield> <type>text</type>
      </para>
      <para>
       Minimum allowed value of the parameter (null for non-numeric
       values)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>max_val</structfield> <type>text</type>
      </para>
      <para>
       Maximum allowed value of the parameter (null for non-numeric
       values)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>enumvals</structfield> <type>text[]</type>
      </para>
      <para>
       Allowed values of an enum parameter (null for non-enum
       values)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>boot_val</structfield> <type>text</type>
      </para>
      <para>
       Parameter value assumed at server startup if the parameter is
       not otherwise set
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reset_val</structfield> <type>text</type>
      </para>
      <para>
       Value that <link linkend="sql-reset"><command>RESET</command></link> would reset the parameter to
       in the current session
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sourcefile</structfield> <type>text</type>
      </para>
      <para>
       Configuration file the current value was set in (null for
       values set from sources other than configuration files, or when
       examined by a user who is neither a superuser or a member of
       <literal>pg_read_all_settings</literal>); helpful when using
       <literal>include</literal> directives in configuration files
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sourceline</structfield> <type>int4</type>
      </para>
      <para>
       Line number within the configuration file the current value was
       set at (null for values set from sources other than configuration files,
       or when examined by a user who is neither a superuser or a member of
       <literal>pg_read_all_settings</literal>).
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pending_restart</structfield> <type>bool</type>
      </para>
      <para>
       <literal>true</literal> if the value has been changed in the
       configuration file but needs a restart; or <literal>false</literal>
       otherwise.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   There are several possible values of <structfield>context</structfield>.
   In order of decreasing difficulty of changing the setting, they are:
  </para>

  <variablelist>
   <varlistentry>
    <!-- PGC_INTERNAL -->
    <term><literal>internal</literal></term>
    <listitem>
     <para>
      These settings cannot be changed directly; they reflect internally
      determined values.  Some of them may be adjustable by rebuilding the
      server with different configuration options, or by changing options
      supplied to <application>initdb</application>.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <!-- PGC_POSTMASTER -->
    <term><literal>postmaster</literal></term>
    <listitem>
     <para>
      These settings can only be applied when the server starts, so any change
      requires restarting the server.  Values for these settings are typically
      stored in the <filename>postgresql.conf</filename> file, or passed on
      the command line when starting the server.  Of course, settings with any
      of the lower <structfield>context</structfield> types can also be
      set at server start time.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <!-- PGC_SIGHUP -->
    <term><literal>sighup</literal></term>
    <listitem>
     <para>
      Changes to these settings can be made in
      <filename>postgresql.conf</filename> without restarting the server.
      Send a <systemitem>SIGHUP</systemitem> signal to the postmaster to
      cause it to re-read <filename>postgresql.conf</filename> and apply
      the changes.  The postmaster will also forward the
      <systemitem>SIGHUP</systemitem> signal to its child processes so that
      they all pick up the new value.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <!-- PGC_SU_BACKEND -->
    <term><literal>superuser-backend</literal></term>
    <listitem>
     <para>
      Changes to these settings can be made in
      <filename>postgresql.conf</filename> without restarting the server.
      They can also be set for a particular session in the connection request
      packet (for example, via <application>libpq</application>'s <literal>PGOPTIONS</literal>
      environment variable), but only if the connecting user is a superuser.
      However, these settings never change in a session after it is started.
      If you change them in <filename>postgresql.conf</filename>, send a
      <systemitem>SIGHUP</systemitem> signal to the postmaster to cause it to
      re-read <filename>postgresql.conf</filename>.  The new values will only
      affect subsequently-launched sessions.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <!-- PGC_BACKEND -->
    <term><literal>backend</literal></term>
    <listitem>
     <para>
      Changes to these settings can be made in
      <filename>postgresql.conf</filename> without restarting the server.
      They can also be set for a particular session in the connection request
      packet (for example, via <application>libpq</application>'s <literal>PGOPTIONS</literal>
      environment variable); any user can make such a change for their session.
      However, these settings never change in a session after it is started.
      If you change them in <filename>postgresql.conf</filename>, send a
      <systemitem>SIGHUP</systemitem> signal to the postmaster to cause it to
      re-read <filename>postgresql.conf</filename>.  The new values will only
      affect subsequently-launched sessions.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <!-- PGC_SUSET -->
    <term><literal>superuser</literal></term>
    <listitem>
     <para>
      These settings can be set from <filename>postgresql.conf</filename>,
      or within a session via the <command>SET</command> command; but only superusers
      can change them via <command>SET</command>.  Changes in
      <filename>postgresql.conf</filename> will affect existing sessions
      only if no session-local value has been established with <command>SET</command>.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <!-- PGC_USERSET -->
    <term><literal>user</literal></term>
    <listitem>
     <para>
      These settings can be set from <filename>postgresql.conf</filename>,
      or within a session via the <command>SET</command> command.  Any user is
      allowed to change their session-local value.  Changes in
      <filename>postgresql.conf</filename> will affect existing sessions
      only if no session-local value has been established with <command>SET</command>.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>

  <para>
   See <xref linkend="config-setting"/> for more information about the various
   ways to change these parameters.
  </para>

  <para>
   This view does not display <link linkend="runtime-config-custom">customized options</link>
   until the extension module that defines them has been loaded.
  </para>

  <para>
   This view cannot be inserted into or deleted from, but it can be updated.  An
   <command>UPDATE</command> applied to a row of <structname>pg_settings</structname>
   is equivalent to executing the <command>SET</command> command on that named
   parameter. The change only affects the value used by the current
   session. If an <command>UPDATE</command> is issued within a transaction
   that is later aborted, the effects of the <command>UPDATE</command> command
   disappear when the transaction is rolled back. Once the surrounding
   transaction is committed, the effects will persist until the end of the
   session, unless overridden by another <command>UPDATE</command> or
   <command>SET</command>.
  </para>

 </sect1>

 <sect1 id="view-pg-shadow">
  <title><structname>pg_shadow</structname></title>

  <indexterm zone="view-pg-shadow">
   <primary>pg_shadow</primary>
  </indexterm>

  <para>
   The view <structname>pg_shadow</structname> exists for backwards
   compatibility: it emulates a catalog that existed in
   <productname>PostgreSQL</productname> before version 8.1.
   It shows properties of all roles that are marked as
   <structfield>rolcanlogin</structfield> in
   <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.
  </para>

  <para>
   The name stems from the fact that this table
   should not be readable by the public since it contains passwords.
   <link linkend="view-pg-user"><structname>pg_user</structname></link>
   is a publicly readable view on
   <structname>pg_shadow</structname> that blanks out the password field.
  </para>

  <table>
   <title><structname>pg_shadow</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       User name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usesysid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       ID of this user
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usecreatedb</structfield> <type>bool</type>
      </para>
      <para>
       User can create databases
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usesuper</structfield> <type>bool</type>
      </para>
      <para>
       User is a superuser
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>userepl</structfield> <type>bool</type>
      </para>
      <para>
       User can initiate streaming replication and put the system in and
       out of backup mode.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usebypassrls</structfield> <type>bool</type>
      </para>
      <para>
       User bypasses every row-level security policy, see
       <xref linkend="ddl-rowsecurity"/> for more information.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>passwd</structfield> <type>text</type>
      </para>
      <para>
       Password (possibly encrypted); null if none.  See
       <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>
       for details of how encrypted passwords are stored.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>valuntil</structfield> <type>timestamptz</type>
      </para>
      <para>
       Password expiry time (only used for password authentication)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>useconfig</structfield> <type>text[]</type>
      </para>
      <para>
       Session defaults for run-time configuration variables
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-shmem-allocations">
  <title><structname>pg_shmem_allocations</structname></title>

  <indexterm zone="view-pg-shmem-allocations">
   <primary>pg_shmem_allocations</primary>
  </indexterm>

  <para>
   The <structname>pg_shmem_allocations</structname> view shows allocations
   made from the server's main shared memory segment.  This includes both
   memory allocated by <productname>postgres</productname> itself and memory
   allocated by extensions using the mechanisms detailed in
   <xref linkend="xfunc-shared-addin" />.
  </para>

  <para>
   Note that this view does not include memory allocated using the dynamic
   shared memory infrastructure.
  </para>

  <table>
   <title><structname>pg_shmem_allocations</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       The name of the shared memory allocation. NULL for unused memory
       and <literal>&lt;anonymous&gt;</literal> for anonymous
       allocations.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>off</structfield> <type>int8</type>
      </para>
      <para>
       The offset at which the allocation starts. NULL for anonymous
       allocations, since details related to them are not known.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>size</structfield> <type>int8</type>
      </para>
      <para>
       Size of the allocation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>allocated_size</structfield> <type>int8</type>
      </para>
      <para>
       Size of the allocation including padding. For anonymous
       allocations, no information about padding is available, so the
       <literal>size</literal> and <literal>allocated_size</literal> columns
       will always be equal. Padding is not meaningful for free memory, so
       the columns will be equal in that case also.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Anonymous allocations are allocations that have been made
   with <literal>ShmemAlloc()</literal> directly, rather than via
   <literal>ShmemInitStruct()</literal> or
   <literal>ShmemInitHash()</literal>.
  </para>

  <para>
   By default, the <structname>pg_shmem_allocations</structname> view can be
   read only by superusers.
  </para>
 </sect1>

 <sect1 id="view-pg-stats">
  <title><structname>pg_stats</structname></title>

  <indexterm zone="view-pg-stats">
   <primary>pg_stats</primary>
  </indexterm>

  <para>
   The view <structname>pg_stats</structname> provides access to
   the information stored in the <link
   linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link>
   catalog.  This view allows access only to rows of
   <link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link> that correspond to tables the
   user has permission to read, and therefore it is safe to allow public
   read access to this view.
  </para>

  <para>
   <structname>pg_stats</structname> is also designed to present the
   information in a more readable format than the underlying catalog
   &mdash; at the cost that its schema must be extended whenever new slot types
   are defined for <link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link>.
  </para>

  <table>
   <title><structname>pg_stats</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attname</structfield>)
      </para>
      <para>
       Name of column described by this row
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>inherited</structfield> <type>bool</type>
      </para>
      <para>
       If true, this row includes inheritance child columns, not just the
       values in the specified table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>null_frac</structfield> <type>float4</type>
      </para>
      <para>
       Fraction of column entries that are null
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>avg_width</structfield> <type>int4</type>
      </para>
      <para>
       Average width in bytes of column's entries
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_distinct</structfield> <type>float4</type>
      </para>
      <para>
       If greater than zero, the estimated number of distinct values in the
       column.  If less than zero, the negative of the number of distinct
       values divided by the number of rows.  (The negated form is used when
       <command>ANALYZE</command> believes that the number of distinct values is
       likely to increase as the table grows; the positive form is used when
       the column seems to have a fixed number of possible values.)  For
       example, -1 indicates a unique column in which the number of distinct
       values is the same as the number of rows.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_vals</structfield> <type>anyarray</type>
      </para>
      <para>
       A list of the most common values in the column. (Null if
       no values seem to be more common than any others.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_freqs</structfield> <type>float4[]</type>
      </para>
      <para>
       A list of the frequencies of the most common values,
       i.e., number of occurrences of each divided by total number of rows.
       (Null when <structfield>most_common_vals</structfield> is.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>histogram_bounds</structfield> <type>anyarray</type>
      </para>
      <para>
       A list of values that divide the column's values into groups of
       approximately equal population.  The values in
       <structfield>most_common_vals</structfield>, if present, are omitted from this
       histogram calculation.  (This column is null if the column data type
       does not have a <literal>&lt;</literal> operator or if the
       <structfield>most_common_vals</structfield> list accounts for the entire
       population.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>correlation</structfield> <type>float4</type>
      </para>
      <para>
       Statistical correlation between physical row ordering and
       logical ordering of the column values.  This ranges from -1 to +1.
       When the value is near -1 or +1, an index scan on the column will
       be estimated to be cheaper than when it is near zero, due to reduction
       of random access to the disk.  (This column is null if the column data
       type does not have a <literal>&lt;</literal> operator.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_elems</structfield> <type>anyarray</type>
      </para>
      <para>
       A list of non-null element values most often appearing within values of
       the column. (Null for scalar types.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_elem_freqs</structfield> <type>float4[]</type>
      </para>
      <para>
       A list of the frequencies of the most common element values, i.e., the
       fraction of rows containing at least one instance of the given value.
       Two or three additional values follow the per-element frequencies;
       these are the minimum and maximum of the preceding per-element
       frequencies, and optionally the frequency of null elements.
       (Null when <structfield>most_common_elems</structfield> is.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>elem_count_histogram</structfield> <type>float4[]</type>
      </para>
      <para>
       A histogram of the counts of distinct non-null element values within the
       values of the column, followed by the average number of distinct
       non-null elements.  (Null for scalar types.)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The maximum number of entries in the array fields can be controlled on a
   column-by-column basis using the <link linkend="sql-altertable"><command>ALTER
   TABLE SET STATISTICS</command></link>
   command, or globally by setting the
   <xref linkend="guc-default-statistics-target"/> run-time parameter.
  </para>

 </sect1>

 <sect1 id="view-pg-stats-ext">
  <title><structname>pg_stats_ext</structname></title>

  <indexterm zone="view-pg-stats-ext">
   <primary>pg_stats_ext</primary>
  </indexterm>

  <para>
   The view <structname>pg_stats_ext</structname> provides access to
   information about each extended statistics object in the database,
   combining information stored in the <link
   linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>
   and <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
   catalogs.  This view allows access only to rows of
   <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link> and <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
   that correspond to tables the user owns, and therefore
   it is safe to allow public read access to this view.
  </para>

  <para>
   <structname>pg_stats_ext</structname> is also designed to present the
   information in a more readable format than the underlying catalogs
   &mdash; at the cost that its schema must be extended whenever new types
   of extended statistics are added to <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>.
  </para>

  <table>
   <title><structname>pg_stats_ext</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>statistics_schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing extended statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>statistics_name</structfield> <type>name</type>
       (references <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>.<structfield>stxname</structfield>)
      </para>
      <para>
       Name of extended statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>statistics_owner</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       Owner of the extended statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>attnames</structfield> <type>name[]</type>
       (references <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attname</structfield>)
      </para>
      <para>
       Names of the columns included in the extended statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>exprs</structfield> <type>text[]</type>
      </para>
      <para>
       Expressions included in the extended statistics object
      </para></entry>
      </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>kinds</structfield> <type>char[]</type>
      </para>
      <para>
       Types of extended statistics object enabled for this record
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_distinct</structfield> <type>pg_ndistinct</type>
      </para>
      <para>
       N-distinct counts for combinations of column values. If greater
       than zero, the estimated number of distinct values in the combination.
       If less than zero, the negative of the number of distinct values divided
       by the number of rows.
       (The negated form is used when <command>ANALYZE</command> believes that
       the number of distinct values is likely to increase as the table grows;
       the positive form is used when the column seems to have a fixed number
       of possible values.)  For example, -1 indicates a unique combination of
       columns in which the number of distinct combinations is the same as the
       number of rows.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>dependencies</structfield> <type>pg_dependencies</type>
      </para>
      <para>
       Functional dependency statistics
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_vals</structfield> <type>text[]</type>
      </para>
      <para>
       A list of the most common combinations of values in the columns.
       (Null if no combinations seem to be more common than any others.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_val_nulls</structfield> <type>bool[]</type>
      </para>
      <para>
       A list of NULL flags for the most common combinations of values.
       (Null when <structfield>most_common_vals</structfield> is.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_freqs</structfield> <type>float8[]</type>
      </para>
      <para>
       A list of the frequencies of the most common combinations,
       i.e., number of occurrences of each divided by total number of rows.
       (Null when <structfield>most_common_vals</structfield> is.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_base_freqs</structfield> <type>float8[]</type>
      </para>
      <para>
       A list of the base frequencies of the most common combinations,
       i.e., product of per-value frequencies.
       (Null when <structfield>most_common_vals</structfield> is.)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The maximum number of entries in the array fields can be controlled on a
   column-by-column basis using the <link linkend="sql-altertable"><command>ALTER
   TABLE SET STATISTICS</command></link> command, or globally by setting the
   <xref linkend="guc-default-statistics-target"/> run-time parameter.
  </para>

 </sect1>

 <sect1 id="view-pg-stats-ext-exprs">
  <title><structname>pg_stats_ext_exprs</structname></title>

  <indexterm zone="view-pg-stats-ext-exprs">
   <primary>pg_stats_ext_exprs</primary>
  </indexterm>

  <para>
   The view <structname>pg_stats_ext_exprs</structname> provides access to
   information about all expressions included in extended statistics objects,
   combining information stored in the <link
   linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>
   and <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
   catalogs.  This view allows access only to rows of
   <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link> and <link linkend="catalog-pg-statistic-ext-data"><structname>pg_statistic_ext_data</structname></link>
   that correspond to tables the user owns, and therefore
   it is safe to allow public read access to this view.
  </para>

  <para>
   <structname>pg_stats_ext_exprs</structname> is also designed to present
   the information in a more readable format than the underlying catalogs
   &mdash; at the cost that its schema must be extended whenever the structure
   of statistics in <structname>pg_statistic_ext</structname> changes.
  </para>

  <table>
   <title><structname>pg_stats_ext_exprs</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of table the statistics object is defined on
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>statistics_schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing extended statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>statistics_name</structfield> <type>name</type>
       (references <link linkend="catalog-pg-statistic-ext"><structname>pg_statistic_ext</structname></link>.<structfield>stxname</structfield>)
      </para>
      <para>
       Name of extended statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>statistics_owner</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       Owner of the extended statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>expr</structfield> <type>text</type>
      </para>
      <para>
       Expression included in the extended statistics object
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>null_frac</structfield> <type>float4</type>
      </para>
      <para>
       Fraction of expression entries that are null
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>avg_width</structfield> <type>int4</type>
      </para>
      <para>
       Average width in bytes of expression's entries
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_distinct</structfield> <type>float4</type>
      </para>
      <para>
       If greater than zero, the estimated number of distinct values in the
       expression.  If less than zero, the negative of the number of distinct
       values divided by the number of rows.  (The negated form is used when
       <command>ANALYZE</command> believes that the number of distinct values is
       likely to increase as the table grows; the positive form is used when
       the expression seems to have a fixed number of possible values.)  For
       example, -1 indicates a unique expression in which the number of distinct
       values is the same as the number of rows.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_vals</structfield> <type>anyarray</type>
      </para>
      <para>
       A list of the most common values in the expression. (Null if
       no values seem to be more common than any others.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_freqs</structfield> <type>float4[]</type>
      </para>
      <para>
       A list of the frequencies of the most common values,
       i.e., number of occurrences of each divided by total number of rows.
       (Null when <structfield>most_common_vals</structfield> is.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>histogram_bounds</structfield> <type>anyarray</type>
      </para>
      <para>
       A list of values that divide the expression's values into groups of
       approximately equal population.  The values in
       <structfield>most_common_vals</structfield>, if present, are omitted from this
       histogram calculation.  (This expression is null if the expression data type
       does not have a <literal>&lt;</literal> operator or if the
       <structfield>most_common_vals</structfield> list accounts for the entire
       population.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>correlation</structfield> <type>float4</type>
      </para>
      <para>
       Statistical correlation between physical row ordering and
       logical ordering of the expression values.  This ranges from -1 to +1.
       When the value is near -1 or +1, an index scan on the expression will
       be estimated to be cheaper than when it is near zero, due to reduction
       of random access to the disk.  (This expression is null if the expression's
       data type does not have a <literal>&lt;</literal> operator.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_elems</structfield> <type>anyarray</type>
      </para>
      <para>
       A list of non-null element values most often appearing within values of
       the expression. (Null for scalar types.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>most_common_elem_freqs</structfield> <type>float4[]</type>
      </para>
      <para>
       A list of the frequencies of the most common element values, i.e., the
       fraction of rows containing at least one instance of the given value.
       Two or three additional values follow the per-element frequencies;
       these are the minimum and maximum of the preceding per-element
       frequencies, and optionally the frequency of null elements.
       (Null when <structfield>most_common_elems</structfield> is.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>elem_count_histogram</structfield> <type>float4[]</type>
      </para>
      <para>
       A histogram of the counts of distinct non-null element values within the
       values of the expression, followed by the average number of distinct
       non-null elements.  (Null for scalar types.)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The maximum number of entries in the array fields can be controlled on a
   column-by-column basis using the <link linkend="sql-altertable"><command>ALTER
   TABLE SET STATISTICS</command></link> command, or globally by setting the
   <xref linkend="guc-default-statistics-target"/> run-time parameter.
  </para>

 </sect1>

 <sect1 id="view-pg-tables">
  <title><structname>pg_tables</structname></title>

  <indexterm zone="view-pg-tables">
   <primary>pg_tables</primary>
  </indexterm>

  <para>
   The view <structname>pg_tables</structname> provides access to
   useful information about each table in the database.
  </para>

  <table>
   <title><structname>pg_tables</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablename</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tableowner</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       Name of table's owner
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablespace</structfield> <type>name</type>
       (references <link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.<structfield>spcname</structfield>)
      </para>
      <para>
       Name of tablespace containing table (null if default for database)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>hasindexes</structfield> <type>bool</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relhasindex</structfield>)
      </para>
      <para>
       True if table has (or recently had) any indexes
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>hasrules</structfield> <type>bool</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relhasrules</structfield>)
      </para>
      <para>
       True if table has (or once had) rules
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>hastriggers</structfield> <type>bool</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relhastriggers</structfield>)
      </para>
      <para>
       True if table has (or once had) triggers
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>rowsecurity</structfield> <type>bool</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relrowsecurity</structfield>)
      </para>
      <para>
       True if row security is enabled on the table
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-timezone-abbrevs">
  <title><structname>pg_timezone_abbrevs</structname></title>

  <indexterm zone="view-pg-timezone-abbrevs">
   <primary>pg_timezone_abbrevs</primary>
  </indexterm>

  <para>
   The view <structname>pg_timezone_abbrevs</structname> provides a list
   of time zone abbreviations that are currently recognized by the datetime
   input routines.  The contents of this view change when the
   <xref linkend="guc-timezone-abbreviations"/> run-time parameter is modified.
  </para>

  <table>
   <title><structname>pg_timezone_abbrevs</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>abbrev</structfield> <type>text</type>
      </para>
      <para>
       Time zone abbreviation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>utc_offset</structfield> <type>interval</type>
      </para>
      <para>
       Offset from UTC (positive means east of Greenwich)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>is_dst</structfield> <type>bool</type>
      </para>
      <para>
       True if this is a daylight-savings abbreviation
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   While most timezone abbreviations represent fixed offsets from UTC,
   there are some that have historically varied in value
   (see <xref linkend="datetime-config-files"/> for more information).
   In such cases this view presents their current meaning.
  </para>

 </sect1>

 <sect1 id="view-pg-timezone-names">
  <title><structname>pg_timezone_names</structname></title>

  <indexterm zone="view-pg-timezone-names">
   <primary>pg_timezone_names</primary>
  </indexterm>

  <para>
   The view <structname>pg_timezone_names</structname> provides a list
   of time zone names that are recognized by <command>SET TIMEZONE</command>,
   along with their associated abbreviations, UTC offsets,
   and daylight-savings status.  (Technically,
   <productname>PostgreSQL</productname> does not use UTC because leap
   seconds are not handled.)
   Unlike the abbreviations shown in <link
   linkend="view-pg-timezone-abbrevs"><structname>pg_timezone_abbrevs</structname></link>, many of these names imply a set of daylight-savings transition
   date rules.  Therefore, the associated information changes across local DST
   boundaries.  The displayed information is computed based on the current
   value of <function>CURRENT_TIMESTAMP</function>.
  </para>

  <table>
   <title><structname>pg_timezone_names</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       Time zone name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>abbrev</structfield> <type>text</type>
      </para>
      <para>
       Time zone abbreviation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>utc_offset</structfield> <type>interval</type>
      </para>
      <para>
       Offset from UTC (positive means east of Greenwich)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>is_dst</structfield> <type>bool</type>
      </para>
      <para>
       True if currently observing daylight savings
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-user">
  <title><structname>pg_user</structname></title>

  <indexterm zone="view-pg-user">
   <primary>pg_user</primary>
  </indexterm>

  <para>
   The view <structname>pg_user</structname> provides access to
   information about database users.  This is simply a publicly
   readable view of
   <link linkend="view-pg-shadow"><structname>pg_shadow</structname></link>
   that blanks out the password field.
  </para>

  <table>
   <title><structname>pg_user</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usename</structfield> <type>name</type>
      </para>
      <para>
       User name
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usesysid</structfield> <type>oid</type>
      </para>
      <para>
       ID of this user
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usecreatedb</structfield> <type>bool</type>
      </para>
      <para>
       User can create databases
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usesuper</structfield> <type>bool</type>
      </para>
      <para>
       User is a superuser
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>userepl</structfield> <type>bool</type>
      </para>
      <para>
       User can initiate streaming replication and put the system in and
       out of backup mode.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usebypassrls</structfield> <type>bool</type>
      </para>
      <para>
       User bypasses every row-level security policy, see
       <xref linkend="ddl-rowsecurity"/> for more information.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>passwd</structfield> <type>text</type>
      </para>
      <para>
       Not the password (always reads as <literal>********</literal>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>valuntil</structfield> <type>timestamptz</type>
      </para>
      <para>
       Password expiry time (only used for password authentication)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>useconfig</structfield> <type>text[]</type>
      </para>
      <para>
       Session defaults for run-time configuration variables
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

 <sect1 id="view-pg-user-mappings">
  <title><structname>pg_user_mappings</structname></title>

  <indexterm zone="view-pg-user-mappings">
   <primary>pg_user_mappings</primary>
  </indexterm>

  <para>
   The view <structname>pg_user_mappings</structname> provides access
   to information about user mappings.  This is essentially a publicly
   readable view of
   <link linkend="catalog-pg-user-mapping"><structname>pg_user_mapping</structname></link>
   that leaves out the options field if the user has no rights to use
   it.
  </para>

  <table>
   <title><structname>pg_user_mappings</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>umid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-user-mapping"><structname>pg_user_mapping</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the user mapping
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-foreign-server"><structname>pg_foreign_server</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the foreign server that contains this mapping
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>srvname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-foreign-server"><structname>pg_foreign_server</structname></link>.<structfield>srvname</structfield>)
      </para>
      <para>
       Name of the foreign server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>umuser</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       OID of the local role being mapped, or zero if the user mapping is public
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usename</structfield> <type>name</type>
      </para>
      <para>
       Name of the local user to be mapped
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>umoptions</structfield> <type>text[]</type>
      </para>
      <para>
       User mapping specific options, as <quote>keyword=value</quote> strings
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   To protect password information stored as a user mapping option,
   the <structfield>umoptions</structfield> column will read as null
   unless one of the following applies:
   <itemizedlist>
    <listitem>
     <para>
      current user is the user being mapped, and owns the server or
      holds <literal>USAGE</literal> privilege on it
     </para>
    </listitem>
    <listitem>
     <para>
      current user is the server owner and mapping is for <literal>PUBLIC</literal>
     </para>
    </listitem>
    <listitem>
     <para>
      current user is a superuser
     </para>
    </listitem>
   </itemizedlist>
  </para>

 </sect1>


 <sect1 id="view-pg-views">
  <title><structname>pg_views</structname></title>

  <indexterm zone="view-pg-views">
   <primary>pg_views</primary>
  </indexterm>

  <para>
   The view <structname>pg_views</structname> provides access to
   useful information about each view in the database.
  </para>

  <table>
   <title><structname>pg_views</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.<structfield>nspname</structfield>)
      </para>
      <para>
       Name of schema containing view
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>viewname</structfield> <type>name</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relname</structfield>)
      </para>
      <para>
       Name of view
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>viewowner</structfield> <type>name</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>rolname</structfield>)
      </para>
      <para>
       Name of view's owner
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>definition</structfield> <type>text</type>
      </para>
      <para>
       View definition (a reconstructed <xref linkend="sql-select"/> query)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>

</chapter>