GENERAL UPGRADING ADVICE FOR ANY VERSION
========================================

Snapshotting is fast (especially if you have JNA installed) and takes
effectively zero disk space until you start compacting the live data
files again.  Thus, best practice is to ALWAYS snapshot before any
upgrade, just in case you need to roll back to the previous version.
(Cassandra version X + 1 will always be able to read data files created
by version X, but the inverse is not necessarily the case.)

When upgrading major versions of Cassandra, you will be unable to
restore snapshots created with the previous major version using the
'sstableloader' tool. You can upgrade the file format of your snapshots
using the provided 'sstableupgrade' tool.

3.7
===

Upgrading
---------
   - A maximum size for SSTables values has been introduced, to prevent out of memory
     exceptions when reading corrupt SSTables. This maximum size can be set via
     max_value_size_in_mb in cassandra.yaml. The default is 256MB, which matches the default
     value of native_transport_max_frame_size_in_mb. SSTables will be considered corrupt if
     they contain values whose size exceeds this limit. See CASSANDRA-9530 for more details.

3.6
=====

New features
------------
   - JMX connections can now use the same auth mechanisms as CQL clients. New options
     in cassandra-env.(sh|ps1) enable JMX authentication and authorization to be delegated
     to the IAuthenticator and IAuthorizer configured in cassandra.yaml. The default settings
     still only expose JMX locally, and use the JVM's own security mechanisms when remote
     connections are permitted. For more details on how to enable the new options, see the
     comments in cassandra-env.sh. A new class of IResource, JMXResource, is provided for
     the purposes of GRANT/REVOKE via CQL. See CASSANDRA-10091 for more details.
     Also, directly setting JMX remote port via the com.sun.management.jmxremote.port system
     property at startup is deprecated. See CASSANDRA-11725 for more details.
   - JSON timestamps are now in UTC and contain the timezone information, see CASSANDRA-11137 for more details.
   - Collision checks are performed when joining the token ring, regardless of whether
     the node should bootstrap. Additionally, replace_address can legitimately be used
     without bootstrapping to help with recovery of nodes with partially failed disks.
     See CASSANDRA-10134 for more details.
   - Key cache will only hold indexed entries up to the size configured by
     column_index_cache_size_in_kb in cassandra.yaml in memory. Larger indexed entries
     will never go into memory. See CASSANDRA-11206 for more details.
   - For tables having a default_time_to_live specifying a TTL of 0 will remove the TTL
     from the inserted or updated values.
   - Startup is now aborted if corrupted transaction log files are found. The details
     of the affected log files are now logged, allowing the operator to decide how
     to resolve the situation.
   - Filtering expressions are made more pluggable and can be added programatically via
     a QueryHandler implementation. See CASSANDRA-11295 for more details.

3.4
=====

New features
------------
    - Internal authentication now supports caching of encrypted credentials.
      Reference cassandra.yaml:credentials_validity_in_ms
    - Remote configuration of auth caches via JMX can be disabled using the
      the system property cassandra.disable_auth_caches_remote_configuration
    - sstabledump tool is added to be 3.0 version of former sstable2json. The tool only
      supports v3.0+ SSTables. See tool's help for more detail.

Upgrading
---------
    - Nothing specific to 3.4 but please see previous versions upgrading section,
      especially if you are upgrading from 2.2.

Deprecation
-----------
    - The mbean interfaces org.apache.cassandra.auth.PermissionsCacheMBean and
      org.apache.cassandra.auth.RolesCacheMBean are deprecated in favor of
      org.apache.cassandra.auth.AuthCacheMBean. This generalized interface is
      common across all caches in the auth subsystem. The specific mbean interfaces
      for each individual cache will be removed in a subsequent major version.


3.2
===

New features
------------
   - We now make sure that a token does not exist in several data directories. This
     means that we run one compaction strategy per data_file_directory and we use
     one thread per directory to flush. Use nodetool relocatesstables to make sure your
     tokens are in the correct place, or just wait and compaction will handle it. See
     CASSANDRA-6696 for more details.
   - bound maximum in-flight commit log replay mutation bytes to 64 megabytes
     tunable via cassandra.commitlog_max_outstanding_replay_bytes
   - Support for type casting has been added to the selection clause.
   - Hinted handoff now supports compression. Reference cassandra.yaml:hints_compression.
     Note: hints compression is currently disabled by default.

Upgrading
---------
   - The compression ratio metrics computation has been modified to be more accurate.
   - Running Cassandra as root is prevented by default.
   - JVM options are moved from cassandra-env.(sh|ps1) to jvm.options file

Deprecation
-----------
   - The Thrift API is deprecated and will be removed in Cassandra 4.0.


3.1
=====

Upgrading
---------
   - The return value of SelectStatement::getLimit as been changed from DataLimits
     to int.
   - Custom index implementation should be aware that the method Indexer::indexes()
     has been removed as its contract was misleading and all custom implementation
     should have almost surely returned true inconditionally for that method.
   - GC logging is now enabled by default (you can disable it in the jvm.options
     file if you prefer).


3.0
===

New features
------------
   - EACH_QUORUM is now a supported consistency level for read requests.
   - Support for IN restrictions on any partition key component or clustering key
     as well as support for EQ and IN multicolumn restrictions has been added to
     UPDATE and DELETE statement.
   - Support for single-column and multi-colum slice restrictions (>, >=, <= and <)
     has been added to DELETE statements
   - nodetool rebuild_index accepts the index argument without
     the redundant table name
   - Materialized Views, which allow for server-side denormalization, is now
     available. Materialized views provide an alternative to secondary indexes
     for non-primary key queries, and perform much better for indexing high
     cardinality columns.
     See http://www.datastax.com/dev/blog/new-in-cassandra-3-0-materialized-views
   - Hinted handoff has been completely rewritten. Hints are now stored in flat
     files, with less overhead for storage and more efficient dispatch.
     See CASSANDRA-6230 for full details.
   - Option to not purge unrepaired tombstones. To avoid users having data resurrected
     if repair has not been run within gc_grace_seconds, an option has been added to
     only allow tombstones from repaired sstables to be purged. To enable, set the
     compaction option 'only_purge_repaired_tombstones':true but keep in mind that if
     you do not run repair for a long time, you will keep all tombstones around which
     can cause other problems.
   - Enabled warning on GC taking longer than 1000ms. See
     cassandra.yaml:gc_warn_threshold_in_ms

Upgrading
---------
   - Clients must use the native protocol version 3 when upgrading from 2.2.X as
     the native protocol version 4 is not compatible between 2.2.X and 3.Y. See
     https://www.mail-archive.com/user@cassandra.apache.org/msg45381.html for details.
   - A new argument of type InetAdress has been added to IAuthenticator::newSaslNegotiator,
     representing the IP address of the client attempting authentication. It will be a breaking
     change for any custom implementations.
   - token-generator tool has been removed.
   - Upgrade to 3.0 is supported from Cassandra 2.1 versions greater or equal to 2.1.9,
     or Cassandra 2.2 versions greater or equal to 2.2.2. Upgrade from Cassandra 2.0 and
     older versions is not supported.
   - The 'memtable_allocation_type: offheap_objects' option has been removed. It should
     be re-introduced in a future release and you can follow CASSANDRA-9472 to know more.
   - Configuration parameter memory_allocator in cassandra.yaml has been removed.
   - The native protocol versions 1 and 2 are not supported anymore.
   - Max mutation size is now configurable via max_mutation_size_in_kb setting in
     cassandra.yaml; the default is half the size commitlog_segment_size_in_mb * 1024.
   - 3.0 requires Java 8u40 or later.
   - Garbage collection options were moved from cassandra-env to jvm.options file.
   - New transaction log files have been introduced to replace the compactions_in_progress
     system table, temporary file markers (tmp and tmplink) and sstable ancerstors.
     Therefore, compaction metadata no longer contains ancestors. Transaction log files
     list sstable descriptors involved in compactions and other operations such as flushing
     and streaming. Use the sstableutil tool to list any sstable files currently involved
     in operations not yet completed, which previously would have been marked as temporary.
     A transaction log file contains one sstable per line, with the prefix "add:" or "remove:".
     They also contain a special line "commit", only inserted at the end when the transaction
     is committed. On startup we use these files to cleanup any partial transactions that were
     in progress when the process exited. If the commit line is found, we keep new sstables
     (those with the "add" prefix) and delete the old sstables (those with the "remove" prefix),
     vice-versa if the commit line is missing. Should you lose or delete these log files,
     both old and new sstable files will be kept as live files, which will result in duplicated
     sstables. These files are protected by incremental checksums so you should not manually
     edit them. When restoring a full backup or moving sstable files, you should clean-up
     any left over transactions and their temporary files first. You can use this command:
      ===> sstableutil -c ks table
     See CASSANDRA-7066 for full details.
   - New write stages have been added for batchlog and materialized view mutations
     you can set their size in cassandra.yaml
   - User defined functions are now executed in a sandbox.
     To use UDFs and UDAs, you have to enable them in cassandra.yaml.
   - New SSTable version 'la' with improved bloom-filter false-positive handling
     compared to previous version 'ka' used in 2.2 and 2.1. Running sstableupgrade
     is not necessary but recommended.
   - Before upgrading to 3.0, make sure that your cluster is in complete agreement
     (schema versions outputted by `nodetool describecluster` are all the same).
   - Schema metadata is now stored in the new `system_schema` keyspace, and
     legacy `system.schema_*` tables are now gone; see CASSANDRA-6717 for details.
   - Pig's support has been removed.
   - Hadoop BulkOutputFormat and BulkRecordWriter have been removed; use
     CqlBulkOutputFormat and CqlBulkRecordWriter instead.
   - Hadoop ColumnFamilyInputFormat and ColumnFamilyOutputFormat have been removed;
     use CqlInputFormat and CqlOutputFormat instead.
   - Hadoop ColumnFamilyRecordReader and ColumnFamilyRecordWriter have been removed;
     use CqlRecordReader and CqlRecordWriter instead.
   - hinted_handoff_enabled in cassandra.yaml no longer supports a list of data centers.
     To specify a list of excluded data centers when hinted_handoff_enabled is set to true,
     use hinted_handoff_disabled_datacenters, see CASSANDRA-9035 for details.
   - The `sstable_compression` and `chunk_length_kb` compression options have been deprecated.
     The new options are `class` and `chunk_length_in_kb`. Disabling compression should now
     be done by setting the new option `enabled` to `false`.
   - The compression option `crc_check_chance` became a top-level table option, but is currently
     enforced only against tables with enabled compression.
   - Only map syntax is now allowed for caching options. ALL/NONE/KEYS_ONLY/ROWS_ONLY syntax
     has been deprecated since 2.1.0 and is being removed in 3.0.0.
   - The 'index_interval' option for 'CREATE TABLE' statements, which has been deprecated
     since 2.1 and replaced with the 'min_index_interval' and 'max_index_interval' options,
     has now been removed.
   - Batchlog entries are now stored in a new table - system.batches.
     The old one has been deprecated.
   - JMX methods set/getCompactionStrategyClass have been removed, use
     set/getCompactionParameters or set/getCompactionParametersJson instead.
   - SizeTieredCompactionStrategy parameter cold_reads_to_omit has been removed.
   - The secondary index API has been comprehensively reworked. This will be a breaking
     change for any custom index implementations, which should now look to implement
     the new org.apache.cassandra.index.Index interface. New syntax has been added to create
     and query row-based indexes, which are not explicitly linked to a single column in the
     base table.


2.2.4
=====

Deprecation
-----------
    - Pig support has been deprecated, and will be removed in 3.0.
      Please see CASSANDRA-10542 for more details.
    - Configuration parameter memory_allocator in cassandra.yaml has been deprecated
      and will be removed in 3.0.0. As mentioned below for 2.2.0, jemalloc is
      automatically preloaded on Unix platforms.

Operations
----------
    - Switching data center or racks is no longer an allowed operation on a node
      which has data. Instead, the node will need to be decommissioned and
      rebootstrapped. If moving from the SimpleSnitch, make sure that the data
      center and rack containing all current nodes is named "datacenter1" and
      "rack1". To override this behaviour use -Dcassandra.ignore_rack=true and/or
      -Dcassandra.ignore_dc=true.
    - Reloading the configuration file of GossipingPropertyFileSnitch has been disabled.

Upgrading
---------
    - The default for the inter-DC stream throughput setting
      (inter_dc_stream_throughput_outbound_megabits_per_sec in cassandra.yaml) is
      the same than the one for intra-DC one (200Mbps) instead of being unlimited.
      Having it unlimited was never intended and was a bug.

New features
------------
    - Time windows in DTCS are now limited to 1 day by default to be able to
      handle bootstrap and repair in a better way. To get the old behaviour,
      increase max_window_size_seconds.
    - DTCS option max_sstable_age_days is now deprecated and defaults to 1000 days.
    - Native protocol server now allows both SSL and non-SSL connections on
      the same port.

2.2.3
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.2 if you are upgrading
      from a previous version.


2.2.2
=====

Changed Defaults
----------------
   - commitlog_total_space_in_mb will use the smaller of 8192, and 1/4
     of the total space of the commitlog volume. (Before: always used
     8192)
   - The following INFO logs were reduced to DEBUG level and will now show
     on debug.log instead of system.log:
      - Memtable flushing actions
      - Commit log replayed files
      - Compacted sstables
      - SStable opening (SSTableReader)

New features
------------
   - Custom QueryHandlers can retrieve the column specifications for the bound
     variables from QueryOptions by using the hasColumnSpecifications()
     and getColumnSpecifications() methods.
   - A new default assynchronous log appender debug.log was created in addition
     to  the system.log appender in order to provide more detailed log debugging.
     In order to disable debug logging, you must comment-out the ASYNCDEBUGLOG
     appender on conf/logback.xml. See CASSANDRA-10241 for more information.


2.2.1
=====

New features
------------
   - COUNT(*) and COUNT(1) can be selected with other columns or functions


2.2
===

Upgrading
---------
   - The authentication & authorization subsystems have been redesigned to
     support role based access control (RBAC), resulting in a change to the
     schema of the system_auth keyspace. See below for more detail.
     For systems already using the internal auth implementations, the process
     for converting existing data during a rolling upgrade is straightforward.
     As each node is restarted, it will attempt to convert any data in the
     legacy tables into the new schema. Until enough nodes to satisfy the
     replication strategy for the system_auth keyspace are upgraded and so have
     the new schema, this conversion will fail with the failure being reported
     in the system log.
     During the upgrade, Cassandra's internal auth classes will continue to use
     the legacy tables, so clients experience no disruption. Issuing DCL
     statements during an upgrade is not supported.
     Once all nodes are upgraded, an operator with superuser privileges should
     drop the legacy tables, system_auth.users, system_auth.credentials and 
     system_auth.permissions. Doing so will prompt Cassandra to switch over to 
     the new tables without requiring any further intervention.
     While the legacy tables are present a restarted node will re-run the data
     conversion and report the outcome so that operators can verify that it is
     safe to drop them.

New features
------------
   - The LIMIT clause applies now only to the number of rows returned to the user,
     not to the number of row queried. By consequence, queries using aggregates will not
     be impacted by the LIMIT clause anymore.
   - Very large batches will now be rejected (defaults to 50kb). This
     can be customized by modifying batch_size_fail_threshold_in_kb.
   - Selecting columns,scalar functions, UDT fields, writetime or ttl together
     with aggregated is now possible. The value returned for the columns,
     scalar functions, UDT fields, writetime and ttl will be the ones for
     the first row matching the query.
   - Windows is now a supported platform. Powershell execution for startup scripts
     is highly recommended and can be enabled via an administrator command-prompt
     with: 'powershell set-executionpolicy unrestricted'
   - It is now possible to do major compactions when using leveled compaction.
     Doing that will take all sstables and compact them out in levels. The
     levels will be non overlapping so doing this will still not be something
     you want to do very often since it might cause more compactions for a while.
     It is also possible to split output when doing a major compaction with
     STCS - files will be split in sizes 50%, 25%, 12.5% etc of the total size.
     This might be a bit better than old major compactions which created one big
     file on disk.
   - A new tool has been added bin/sstableverify that checks for errors/bitrot
     in all sstables.  Unlike scrub, this is a non-invasive tool.
   - Authentication & Authorization APIs have been updated to introduce
     roles. Roles and Permissions granted to them are inherited, supporting
     role based access control. The role concept supercedes that of users
     and CQL constructs such as CREATE USER are deprecated but retained for
     compatibility. The requirement to explicitly create Roles in Cassandra
     even when auth is handled by an external system has been removed, so
     authentication & authorization can be delegated to such systems in their
     entirety.
   - In addition to the above, Roles are also first class resources and can be the
     subject of permissions. Users (roles) can now be granted permissions on other
     roles, including CREATE, ALTER, DROP & AUTHORIZE, which removesthe need for
     superuser privileges in order to perform user/role management operations.
   - Creators of database resources (Keyspaces, Tables, Roles) are now automatically
     granted all permissions on them (if the IAuthorizer implementation supports
     this).
   - SSTable file name is changed. Now you don't have Keyspace/CF name
     in file name. Also, secondary index has its own directory under parent's
     directory.
   - Support for user-defined functions and user-defined aggregates have
     been added to CQL.
     ************************************************************************
     IMPORTANT NOTE: user-defined functions can be used to execute
     arbitrary and possibly evil code in Cassandra 2.2, and are
     therefore disabled by default.  To enable UDFs edit
     cassandra.yaml and set enable_user_defined_functions to true.

     CASSANDRA-9402 will add a security manager for UDFs in Cassandra
     3.0.  This will inherently be backwards-incompatible with any 2.2
     UDF that perform insecure operations such as opening a socket or
     writing to the filesystem.
     ************************************************************************
   - Row-cache is now fully off-heap.
   - jemalloc is now automatically preloaded and used on Linux and OS-X if
     installed.
   - Please ensure on Unix platforms that there is no libjnadispath.so
     installed which is accessible by Cassandra. Old versions of
     libjna packages (< 4.0.0) will cause problems - e.g. Debian Wheezy
     contains libjna versin 3.2.x.
   - The node now keeps up when streaming is failed during bootstrapping. You can
     use new `nodetool bootstrap resume` command to continue streaming after resolving
     an issue.
   - Protocol version 4 specifies that bind variables do not require having a
     value when executing a statement. Bind variables without a value are
     called 'unset'. The 'unset' bind variable is serialized as the int
     value '-2' without following bytes.
     In an EXECUTE or BATCH request an unset bind value does not modify the value and
     does not create a tombstone, an unset bind ttl is treated as 'unlimited',
     an unset bind timestamp is treated as 'now', an unset bind counter operation
     does not change the counter value.
     Unset tuple field, UDT field and map key are not allowed.
     In a QUERY request an unset limit is treated as 'unlimited'.
     Unset WHERE clauses with unset partition column, clustering column
     or index column are not allowed.
   - New `ByteType` (cql tinyint). 1-byte signed integer
   - New `ShortType` (cql smallint). 2-byte signed integer
   - New `SimpleDateType` (cql date). 4-byte unsigned integer
   - New `TimeType` (cql time). 8-byte long
   - The toDate(timeuuid), toTimestamp(timeuuid) and toUnixTimestamp(timeuuid) functions have been added to allow
     to convert from timeuuid into date type, timestamp type and bigint raw value.
     The functions unixTimestampOf(timeuuid) and dateOf(timeuuid) have been deprecated.
   - The toDate(timestamp) and toUnixTimestamp(timestamp) functions have been added to allow
     to convert from timestamp into date type and bigint raw value.
   - The toTimestamp(date) and toUnixTimestamp(date) functions have been added to allow
     to convert from date into timestamp type and bigint raw value.
   - SizeTieredCompactionStrategy parameter cold_reads_to_omit has been removed.
   - The default JVM flag -XX:+PerfDisableSharedMem will cause the following tools JVM
     to stop working: jps, jstack, jinfo, jmc, jcmd as well as 3rd party tools like Jolokia.
     If you wish to use these tools you can comment this flag out in cassandra-env.{sh,ps1}

Upgrading
---------
   - Thrift rpc is no longer being started by default.
     Set `start_rpc` parameter to `true` to enable it.
   - Pig's CqlStorage has been removed, use CqlNativeStorage instead
   - Pig's CassandraStorage has been deprecated. CassandraStorage
     should only be used against tables created via thrift.
     Use CqlNativeStorage for all other tables.
   - IAuthenticator been updated to remove responsibility for user/role
     maintenance and is now solely responsible for validating credentials,
     This is primarily done via SASL, though an optional method exists for
     systems which need support for the Thrift login() method.
   - IRoleManager interface has been added which takes over the maintenance
     functions from IAuthenticator. IAuthorizer is mainly unchanged. Auth data
     in systems using the stock internal implementations PasswordAuthenticator
     & CassandraAuthorizer will be automatically converted during upgrade,
     with minimal operator intervention required. Custom implementations will
     require modification, though these can be used in conjunction with the
     stock CassandraRoleManager so providing an IRoleManager implementation
     should not usually be necessary.
   - Fat client support has been removed since we have push notifications to clients
   - cassandra-cli has been removed. Please use cqlsh instead.
   - YamlFileNetworkTopologySnitch has been removed; switch to
     GossipingPropertyFileSnitch instead.
   - CQL2 has been removed entirely in this release (previously deprecated
     in 2.0.0). Please switch to CQL3 if you haven't already done so.
   - The results of CQL3 queries containing an IN restriction will be ordered
     in the normal order and not anymore in the order in which the column values were
     specified in the IN restriction.
   - Some secondary index queries with restrictions on non-indexed clustering
     columns were not requiring ALLOW FILTERING as they should. This has been
     fixed, and those queries now require ALLOW FILTERING (see CASSANDRA-8418
     for details).
   - The SSTableSimpleWriter and SSTableSimpleUnsortedWriter classes have been
     deprecated and will be removed in the next major Cassandra release. You
     should use the CQLSSTableWriter class instead.
   - The sstable2json and json2sstable tools have been deprecated and will be
     removed in the next major Cassandra release. See CASSANDRA-9618
     (https://issues.apache.org/jira/browse/CASSANDRA-9618) for details.
   - nodetool enablehandoff will no longer support a list of data centers starting
     with the next major release. Two new commands will be added, enablehintsfordc and disablehintsfordc,
     to exclude data centers from using hinted handoff when the global status is enabled.
     In cassandra.yaml, hinted_handoff_enabled will no longer support a list of data centers starting
     with the next major release. A new setting will be added, hinted_handoff_disabled_datacenters,
     to exclude data centers when the global status is enabled, see CASSANDRA-9035 for details.


2.1.13
======

New features
------------
    - New options for cqlsh COPY FROM and COPY TO, see CASSANDRA-9303 for details.

2.1.10
=====

New features
------------
   - The syntax TRUNCATE TABLE X is now accepted as an alias for TRUNCATE X


2.1.9
=====

Upgrading
---------
    - cqlsh will now display timestamps with a UTC timezone. Previously,
      timestamps were displayed with the local timezone.
    - Commit log files are no longer recycled by default, due to negative
      performance implications. This can be enabled again with the 
      commitlog_segment_recycling option in your cassandra.yaml 
    - JMX methods set/getCompactionStrategyClass have been deprecated, use
      set/getCompactionParameters/set/getCompactionParametersJson instead

2.1.8
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.1 if you are upgrading
      from a previous version.


2.1.7
=====


2.1.6
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.1 if you are upgrading
      from a previous version.


2.1.5
=====

Upgrading
---------
    - The option to omit cold sstables with size tiered compaction has been
      removed - it is almost always better to use date tiered compaction for
      workloads that have cold data.

2.1.4
=====

Upgrading
---------
The default JMX config now listens to localhost only. You must enable
the other JMX flags in cassandra-env.sh manually.


2.1.3
=====

Upgrading
---------
    - Prepending a list to a list collection was erroneously resulting in
      the prepended list being reversed upon insertion.  If you were depending
      on this buggy behavior, note that it has been corrected.
    - Incremental replacement of compacted SSTables has been disabled for this
      release.


2.1.2
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.1 if you are upgrading
      from a previous version.


2.1.1
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.1 if you are upgrading
      from a previous version.

New features
------------
   - Netty support for epoll on linux is now enabled.  If for some
     reason you want to disable it pass, the following system property
     -Dcassandra.native.epoll.enabled=false


2.1
===

New features
------------
   - Default data and log locations have changed.  If not set in
     cassandra.yaml, the data file directory, commitlog directory,
     and saved caches directory will default to $CASSANDRA_HOME/data/data,
     $CASSANDRA_HOME/data/commitlog, and $CASSANDRA_HOME/data/saved_caches,
     respectively.  The log directory now defaults to $CASSANDRA_HOME/logs.
     If not set, $CASSANDRA_HOME, defaults to the top-level directory of
     the installation.
     Note that this should only affect source checkouts and tarballs.
     Deb and RPM packages will continue to use /var/lib/cassandra and
     /var/log/cassandra in cassandra.yaml.
   - SSTable data directory name is slightly changed. Each directory will
     have hex string appended after CF name, e.g.
         ks/cf-5be396077b811e3a3ab9dc4b9ac088d/
     This hex string part represents unique ColumnFamily ID.
     Note that existing directories are used as is, so only newly created
     directories after upgrade have new directory name format.
   - Saved key cache files also have ColumnFamily ID in their file name.
   - It is now possible to do incremental repairs, sstables that have been
     repaired are marked with a timestamp and not included in the next
     repair session. Use nodetool repair -par -inc to use this feature.
     A tool to manually mark/unmark sstables as repaired is available in
     tools/bin/sstablerepairedset. This is particularly important when
     using LCS, or any data not repaired in your first incremental repair
     will be put back in L0.
   - Bootstrapping now ensures that range movements are consistent,
     meaning the data for the new node is taken from the node that is no
     longer a responsible for that range of keys.
     If you want the old behavior (due to a lost node perhaps)
     you can set the following property (-Dcassandra.consistent.rangemovement=false)
   - It is now possible to use quoted identifiers in triggers' names.
     WARNING: if you previously used triggers with capital letters in their
     names, then you must quote them from now on.
   - Improved stress tool (http://goo.gl/OTNqiQ)
   - New incremental repair option (http://goo.gl/MjohJp, http://goo.gl/f8jSme)
   - Incremental replacement of compacted SSTables (http://goo.gl/JfDBGW)
   - The row cache can now cache only the head of partitions (http://goo.gl/6TJPH6)
   - Off-heap memtables (http://goo.gl/YT7znJ)
   - CQL improvements and additions: User-defined types, tuple types, 2ndary
     indexing of collections, ... (http://goo.gl/kQl7GW)

Upgrading
---------
   - commitlog_sync_batch_window_in_ms behavior has changed from the
     maximum time to wait between fsync to the minimum time.  We are 
     working on making this more user-friendly (see CASSANDRA-9533) but in the
     meantime, this means 2.1 needs a much smaller batch window to keep
     writer threads from starving.  The suggested default is now 2ms.
   - Rolling upgrades from anything pre-2.0.7 is not supported. Furthermore
     pre-2.0 sstables are not supported. This means that before upgrading
     a node on 2.1, this node must be started on 2.0 and
     'nodetool upgdradesstables' must be run (and this even in the case
     of not-rolling upgrades).
   - For size-tiered compaction users, Cassandra now defaults to ignoring
     the coldest 5% of sstables.  This can be customized with the
     cold_reads_to_omit compaction option; 0.0 omits nothing (the old
     behavior) and 1.0 omits everything.
   - Multithreaded compaction has been removed.
   - Counters implementation has been changed, replaced by a safer one with
     less caveats, but different performance characteristics. You might have
     to change your data model to accomodate the new implementation.
     (See https://issues.apache.org/jira/browse/CASSANDRA-6504 and the
     blog post at http://goo.gl/qj8iQl for details).
   - (per-table) index_interval parameter has been replaced with
     min_index_interval and max_index_interval paratemeters. index_interval
     has been deprecated.
   - support for supercolumns has been removed from json2sstable


2.0.11
======

Upgrading
---------
    - Nothing specific to this release, but refer to previous entries if you
      are upgrading from a previous version.

New features
------------
    - DateTieredCompactionStrategy added, optimized for time series data and groups
      data that is written closely in time (CASSANDRA-6602 for details). Consider
      this experimental for now.


2.0.10
======

New features
------------
    - CqlPaginRecordReader and CqlPagingInputFormat have both been removed.
      Use CqlInputFormat instead.
    - If you are using Leveled Compaction, you can now disable doing size-tiered
      compaction in L0 by starting Cassandra with -Dcassandra.disable_stcs_in_l0
      (see CASSANDRA-6621 for details).
    - Shuffle and taketoken have been removed.  For clusters that choose to
      upgrade to vnodes, creating a new datacenter with vnodes and migrating is
      recommended. See http://goo.gl/Sna2S1 for further information.


2.0.9
=====

Upgrading
---------
    - Default values for read_repair_chance and local_read_repair_chance have been
      swapped. Namely, default read_repair_chance is now set to 0.0, and default
      local_read_repair_chance to 0.1.
    - Queries selecting only CQL static columns were (mistakenly) not returning one
      result per row in the partition. This has been fixed and a SELECT DISTINCT
      can be used when only the static column of a partition needs to be fetch
      without fetching the whole partition. But if you use static columns, please
      make sure this won't affect you (see CASSANDRA-7305 for details).


2.0.8
=====

New features
------------
    - New snitches have been used for users of Google Compute Engine and of
      Cloudstack.

Upgrading
---------
    - Nothing specific to this release, but please see 2.0.7 if you are upgrading
      from a previous version.


2.0.7
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.0.6 if you are upgrading
      from a previous version.


2.0.6
=====

New features
------------
    - CQL now support static columns, allows to batch multiple conditional updates
      and has a new syntax for slicing over multiple clustering columns
      (http://goo.gl/B6qz4j).
    - Repair can be restricted to a set of nodes using the -hosts option in nodetool.
    - A new 'nodetool taketoken' command relocate tokens with vnodes.
    - Hinted handoff can be enabled only for some data-centers (see
      hinted_handoff_enabled in cassandra.yaml)

Upgrading
---------
    - Nothing specific to this release, but please see 2.0.5 if you are upgrading
      from a previous version.


2.0.5
=====

New features
------------
    - Batchlog replay can be, and is throttled by default now.
      See batchlog_replay_throttle_in_kb setting in cassandra.yaml.
    - Scrub can now optionally skip corrupt counter partitions. Please note
      that this will lead to the loss of all the counter updates in the skipped
      partition. See the --skip-corrupted option.

Upgrading
---------
    - If your cluster began on a version before 1.2, check that your secondary
      index SSTables are on version 'ic' before upgrading.  If not, run
      'nodetool upgradesstables' if on 1.2.14 or later, or run 'nodetool
      upgradesstables ks cf' with the keyspace and secondary index named
      explicitly otherwise.  If you don't do this and upgrade to 2.0.x and it
      refuses to start because of 'hf' version files in the secondary index,
      you will need to delete/move them out of the way and recreate the index
      when 2.0.x starts.


2.0.3
=====

New features
------------
    - It's now possible to configure the maximum allowed size of the native
      protocol frames (native_transport_max_frame_size_in_mb in the yaml file).

Upgrading
---------
    - NaN and Infinity are new valid floating point constants in CQL3 and are now reserved
      keywords. In the unlikely case you were using one of them as an identifier (for a
      column, a keyspace or a table), you will now have to double-quote them (see
      http://cassandra.apache.org/doc/cql3/CQL.html#identifiers for "quoted identifiers").
    - The IEndpointStateChangeSubscriber has a new method, beforeChange, that
      any custom implemenations using the class will need to implement.


2.0.2
=====

New features
------------
    - Speculative retry defaults to 99th percentile
      (See blog post at http://www.datastax.com/dev/blog/rapid-read-protection-in-cassandra-2-0-2)
    - Configurable metrics reporting
      (see conf/metrics-reporter-config-sample.yaml)
    - Compaction history and stats are now saved to system keyspace
      (system.compaction_history table). You can access historiy via
      new 'nodetool compactionhistory' command or CQL.

Upgrading
---------
    - Nodetool defaults to Sequential mode for repair operations


2.0.1
=====
Upgrading
---------
    - The default memtable allocation has changed from 1/3 of heap to 1/4
      of heap.  Also, default (single-partition) read and write timeouts
      have been reduced from 10s to 5s and 2s, respectively.


2.0.0
=====

Upgrading
---------
    - Java 7 is now *required*!
    - Upgrading is ONLY supported from Cassandra 1.2.9 or later. This
      goes for sstable compatibility as well as network.  When
      upgrading from an earlier release, upgrade to 1.2.9 first and
      run upgradesstables before proceeding to 2.0.
    - CAS and new features in CQL such as DROP COLUMN assume that cell
      timestamps are microseconds-since-epoch.  Do not use these
      features if you are using client-specified timestamps with some
      other source.
    - Replication and strategy options do not accept unknown options anymore.
      This was already the case for CQL3 in 1.2 but this is now the case for
      thrift too.
    - auto_bootstrap of a single-token node with no initial_token will
      now pick a random token instead of bisecting an existing token
      range.  We recommend upgrading to vnodes; failing that, we
      recommend specifying initial_token.
    - reduce_cache_sizes_at, reduce_cache_capacity_to, and
      flush_largest_memtables_at options have been removed from cassandra.yaml.
    - CacheServiceMBean.reduceCacheSizes() has been removed.
      Use CacheServiceMBean.set{Key,Row}CacheCapacityInMB() instead.
    - authority option in cassandra.yaml has been deprecated since 1.2.0,
      but it has been completely removed in 2.0. Please use 'authorizer' option.
    - ASSUME command has been removed from cqlsh. Use CQL3 blobAsType() and
      typeAsBlob() conversion functions instead.
      See https://cassandra.apache.org/doc/cql3/CQL.html#blobFun for details.
    - Inputting blobs as string constants is now fully deprecated in
      favor of blob constants. Make sure to update your applications to use
      the new syntax while you are still on 1.2 (which supports both string
      and blob constants for blob input) before upgrading to 2.0.
    - index_interval is now moved to ColumnFamily property. You can change value
      with ALTER TABLE ... WITH statement and SSTables written after that will
      have new value. When upgrading, Cassandra will pick up the value defined in
      cassanda.yaml as the default for existing ColumnFamilies, until you explicitly
      set the value for those.
    - The deprecated native_transport_min_threads option has been removed in
      Cassandra.yaml.

Operations
----------
    - VNodes are enabled by default in cassandra.yaml.  initial_token
      for non-vnode deployments has been removed from the example
      yaml, but is still respected if specified.
    - Major compactions, cleanup, scrub, and upgradesstables will interrupt
      any in-progress compactions (but not repair validations) when invoked.
    - Disabling autocompactions by setting min/max compaction threshold to 0
      has been deprecated, instead, use the nodetool commands 'disableautocompaction'
      and 'enableautocompaction' or set the compaction strategy option enabled = false
    - ALTER TABLE DROP has been reenabled for CQL3 tables and has new semantics now.
      See https://cassandra.apache.org/doc/cql3/CQL.html#alterTableStmt and
      https://issues.apache.org/jira/browse/CASSANDRA-3919 for details.
    - CAS uses gc_grace_seconds to determine how long to keep unused paxos
      state around for, or a minimum of three hours.
    - A new hints created metric is tracked per target, replacing countPendingHints
    - After performance testing for CASSANDRA-5727, the default LCS filesize
      has been changed from 5MB to 160MB.
    - cqlsh DESCRIBE SCHEMA no longer outputs the schema of system_* keyspaces;
      use DESCRIBE FULL SCHEMA if you need the schema of system_* keyspaces.
    - CQL2 has been deprecated, and will be removed entirely in 2.2. See
      CASSANDRA-5918 for details.
    - Commit log archiver now assumes the client time stamp to be in microsecond
      precision, during restore. Please refer to commitlog_archiving.properties.


Features
--------
    - Lightweight transactions
      (http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0)
    - Alias support has been added to CQL3 SELECT statement. Refer to
      CQL3 documentation (http://cassandra.apache.org/doc/cql3/CQL.html) for details.
    - JEMalloc support (see memory_allocator in cassandra.yaml)
    - Experimental triggers support.  See examples/ for how to use.  "Experimental"
      means "tied closely to internal data structures; we plan to decouple this in
      the future, which will probably break triggers written against this initial
      API."
    - Numerous improvements to CQL3 and a new version of the native protocol. See
      http://www.datastax.com/dev/blog/cql-in-cassandra-2-0 for details.

1.2.11
======

Features
--------
    - Added a new consistency level, LOCAL_ONE, that forces all CL.ONE operations to
      execute only in the local datacenter.
    - New replace_address to supplant the (now removed) replace_token and
      replace_node workflows to replace a dead node in place.  Works like the
      old options, but takes the IP address of the node to be replaced.

1.2.9
=====

Features
--------
    - A history of executed nodetool commands is now captured.
      It can be found in ~/.cassandra/nodetool.history. Other tools output files
      (cli and cqlsh history, .cqlshrc) are now centralized in ~/.cassandra, as well.
    - A new sstablesplit utility allows to split large sstables offline.


1.2.8
=====

Upgrading
---------
    - Nothing specific to this release, but please see 1.2.7 if you are upgrading
      from a previous version.


1.2.7
=====

Upgrading
---------
    - If you have decommissioned a node in the past 72 hours, it is imperative
      that you not upgrade until such time has passed, or do a full cluster
      restart (not rolling) before beginning the upgrade.  This only applies to
      decommission, not removetoken.


1.2.6
=====

Upgrading
---------
    - hinted_handoff_throttle_in_kb is now reduced by a factor
      proportional to the number of nodes in the cluster (see
      https://issues.apache.org/jira/browse/CASSANDRA-5272).
    - CQL3 syntax for CREATE CUSTOM INDEX has been updated. See CQL3
      documentation for details.


1.2.5
=====

Features
--------
    - Custom secondary index support has been added to CQL3. Refer to
      CQL3 documentation (http://cassandra.apache.org/doc/cql3/CQL.html)
      for details and examples.

Upgrading
---------
    - The native CQL transport is enabled by default on part 9042.


1.2.4
=====

Upgrading
---------
    - 'nodetool upgradesstables' now only upgrades/rewrites sstables that are
      not on the current version (which is usually what you want). Use the new
      -a flag to recover the old behavior of rewriting all sstables.

Features
--------
    - superuser setup delay (10 seconds) can now be overridden using
      'cassandra.superuser_setup_delay_ms' property.


1.2.3
=====

Upgrading
---------
    - CQL3 used to be case-insensitive for property map key in ALTER and CREATE
      statements. In other words:
        CREATE KEYSPACE test WITH replication = { 'CLASS' : 'SimpleStrategy',
                                                  'REPLICATION_FACTOR' : '1' }
      was allowed. However, this was not consistent with the fact that string
      literal are case sensitive in every other places and more importantly this
      break NetworkTopologyStrategy for which DC names are case sensitive. Those
      property map key are now case sensitive. So the statement above should be
      changed to:
        CREATE KEYSPACE test WITH replication = { 'class' : 'SimpleStrategy',
                                                  'replication_factor' : '1' }


1.2.2
=====

Upgrading
---------
    - CQL3 type validation for constants has been fixed, which may require
      fixing queries that were relying on the previous loose validation. Please
      refer to the CQL3 documentation (http://cassandra.apache.org/doc/cql3/CQL.html)
      and in particular the changelog section for more details. Please note in
      particular that inputing blobs as strings constants is now deprecated (in
      favor of blob constants) and its support will be removed in a future
      version.

Features
--------
    - Built-in CQL3-based implementations of IAuthenticator (PasswordAuthenticator)
      and IAuthorizer (CassandraAuthorizer) have been added. PasswordAuthenticator
      stores usernames and hashed passwords in system_auth.credentials table;
      CassandraAuthorizer stores permissions in system_auth.permissions table.
    - system_auth keyspace is now alterable via ALTER KEYSPACE queries.
      The default is SimpleStrategy with replication_factor of 1, but it's
      advised to raise RF to at least 3 or 5, since CL.QUORUM is used for all
      auth-related queries. It's also possible to change the strategy to NTS.
    - Permissions caching with time-based expiration policy has been added to reduce
      performance impact of authorization. Permission validity can be configured
      using 'permissions_validity_in_ms' setting in cassandra.yaml. The default
      is 2000 (2 seconds).
    - SimpleAuthenticator and SimpleAuthorizer examples have been removed. Please
      look at CassandraAuthorizer/PasswordAuthenticator instead.


1.2.1
=====

Upgrading
---------
    - In CQL3, date string are no longer accepted as timeuuid value since a
      date string is not a correct representation of a timeuuid. Instead, new
      methods (minTimeuuid, maxTimeuuid, now, dateOf, unixTimestampOf) have been
      introduced to make working on timeuuid from date string easy. cqlsh also
      does not display timeuuid as date string (since this is a lossy
      representation), but the new dateOf method can be used instead. Please
      refer to the reference documentation (http://cassandra.apache.org/doc/cql3/CQL.html)
      for more detail.
    - For client implementors: CQL3 client using the thrift interface should
      use the new execute_cql3_query, prepare_cql3_query and execute_prepared_cql3_query
      since 1.2.0. However, Cassandra 1.2.0 was not complaining if CQL3 was set
      through set_cql_version but the now CQL2 only methods were used. This is
      now the case.
    - Queries that uses unrecognized or bad compaction or replication strategy
      options are now refused (instead of simply logging a warning).


1.2
===

Upgrading
---------
    - IAuthenticator interface has been updated to support dynamic
      user creation, modification and removal. Users, even when stored
      externally, now have to be explicitly created using
      CREATE USER query first. AllowAllAuthenticator and SimpleAuthenticator
      have been updated for the new interface, but you'll have to update
      your old IAuthenticator implementations for 1.2. To ease this process,
      a new abstract LegacyAuthenticator class has been added - subclass it
      in your old IAuthenticator implementaion and everything should just work
      (this only affects users who implemented custom authenticators).
    - IAuthority interface has been deprecated in favor of IAuthorizer.
      AllowAllAuthority and SimpleAuthority have been renamed to
      AllowAllAuthorizer and SimpleAuthorizer, respectively. In order to
      simplify the upgrade to the new interface, a new abstract
      LegacyAuthorizer has been added - you should subclass it in your
      old IAuthority implementation and everything should just work
      (this only affects users who implemented custom authorities).
      'authority' setting in cassandra.yaml has been renamed to 'authorizer',
      'authority' is no longer recognized. This affects all upgrading users.
    - 1.2 is NOT network-compatible with versions older than 1.0. That
      means if you want to do a rolling, zero-downtime upgrade, you'll need
      to upgrade first to 1.0.x or 1.1.x, and then to 1.2.  1.2 retains
      the ability to read data files from Cassandra versions at least
      back to 0.6, so a non-rolling upgrade remains possible with just
      one step.
    - The default partitioner for new clusters is Murmur3Partitioner,
      which is about 10% faster for index-intensive workloads.  Partitioners
      cannot be changed once data is in the cluster, however, so if you are
      switching to the 1.2 cassandra.yaml, you should change this to
      RandomPartitioner or whatever your old partitioner was.
    - If you using counters and upgrading from a version prior to
      1.1.6, you should drain existing Cassandra nodes prior to the
      upgrade to prevent overcount during commitlog replay (see
      CASSANDRA-4782).  For non-counter uses, drain is not required
      but is a good practice to minimize restart time.
    - Tables using LeveledCompactionStrategy will default to not
      creating a row-level bloom filter.  The default in older versions
      of Cassandra differs; you should manually set the false positive
      rate to 1.0 (to disable) or 0.01 (to enable, if you make many
      requests for rows that do not exist).
    - The hints schema was changed from 1.1 to 1.2. Cassandra automatically
      snapshots and then truncates the hints column family as part of
      starting up 1.2 for the first time.  Additionally, upgraded nodes
      will not store new hints destined for older (pre-1.2) nodes. It is
      therefore recommended that you perform a cluster upgrade when all
      nodes are up. Because hints will be lost, a cluster-wide repair (with
      -pr) is recommended after upgrade of all nodes.
    - The `nodetool removetoken` command (and corresponding JMX operation)
      have been renamed to `nodetool removenode`.  This function is
      incompatible with the earlier `nodetool removetoken`, and attempts to
      remove nodes in this way with a mixed 1.1 (or lower) / 1.2 cluster,
      is not supported.
    - The somewhat ill-conceived CollatingOrderPreservingPartitioner
      has been removed. Use Murmur3Partitioner (recommended) or
      ByteOrderedPartitioner instead.
    - Global option hinted_handoff_throttle_delay_in_ms has been removed.
      hinted_handoff_throttle_in_kb has been added instead.
    - The default bloom filter fp chance has been increased to 1%.
      This will save about 30% of the memory used by the old default.
      Existing columnfamilies will retain their old setting.
    - The default partitioner (for new clusters; the partitioner cannot be
      changed in existing clusters) was changed from RandomPartitioner to
      Murmur3Partitioner which provides faster hashing as well as improved
      performance with secondary indexes.
    - The default version of CQL (and cqlsh) is now CQL3. CQL2 is still
      available but you will have to use the thrift set_cql_version method
      (that is already supported in 1.1) to use CQL2. For cqlsh, you will need
      to use 'cqlsh -2'.
    - CQL3 is now considered final in this release. Compared to the beta
      version that is part of 1.1, this final version has a few additions
      (collections), but also some (incompatible) changes in the syntax for the
      options of the create/alter keyspace/table statements. Typically, the
      syntax to create a keyspace is now:
        CREATE KEYSPACE ks WITH replication = { 'class' : 'SimpleStrategy',
                                                'replication_factor' : 2 };
      Also, the consistency level cannot be set in the language anymore, but is
      at the protocol level.
      Please refer to the CQL3 documentation (http://cassandra.apache.org/doc/cql3/CQL.html)
      for details.
    - In CQL3, the DROP behavior from ALTER TABLE has currently been removed
      (because it was not correctly implemented). We hope to add it back soon
      (Cassandra 1.2.1 or 1.2.2)

Features
--------
    - Cassandra can now handle concurrent CREATE TABLE schema changes
      as well as other updates
    - rpc_timeout has been split up to allow finer-grained control
      on timeouts for different operation types
    - num_tokens can now be specified in cassandra.yaml. This defines the
      number of tokens assigned to the host on the ring (default: 1).
      Also specifying initial_token will override any num_tokens setting.
    - disk_failure_policy allows blacklisting failed disks in JBOD
      configuration instead of erroring out indefinitely
    - event tracing can be configured per-connection ("trace_next_query")
      or globally/probabilistically ("nodetool settraceprobability")
    - Atomic batches are now supported server side, where Cassandra will
      guarantee that (at the price of pre-writing the batch to another node
      first), all mutations in the batch will be applied, even if the
      coordinator fails mid-batch.
    - new IAuthorizer interface has replaced the old IAuthority. IAuthorizer
      allows dynamic permission management via new CQL3 statements:
      GRANT, REVOKE, LIST PERMISSIONS. A native implementation storing
      the permissions in Cassandra is being worked on and we expect to
      include it in 1.2.1 or 1.2.2.
    - IAuthenticator interface has been updated to support dynamic user
      creation, modification and removal via new CQL3 statements:
      CREATE USER, ALTER USER, DROP USER, LIST USERS. A native implementation
      that stores users in Cassandra itself is being worked on and is expected to
      become part of 1.2.1 or 1.2.2.


1.1.5
=====

Upgrading
---------
    - Nothing specific to this release, but please see 1.1 if you are upgrading
      from a previous version.


1.1.4
=====

Upgrading
---------
    - Nothing specific to this release, but please see 1.1 if you are upgrading
      from a previous version.


1.1.3
=====

Upgrading
---------
    - Running "nodetool upgradesstables" after upgrading is recommended
      if you use Counter columnfamilies.

Features
--------
    - the cqlsh COPY command can now export to CSV flat files
    - added a new tools/bin/token-generator to facilitate generating evenly distributed tokens


1.1.2
=====

Upgrading
---------
    - If you have column families using the LeveledCompactionStrategy, you should run scrub on those column families.

Features
--------
    - cqlsh has a new COPY command to load data from CSV flat files


1.1.1
=====

Upgrading
---------
    - Nothing specific to this release, but please see 1.1 if you are upgrading
      from a previous version.

Features
--------
    - Continuous commitlog archiving and point-in-time recovery.
      See conf/commitlog_archiving.properties
    - Incremental repair by token range, exposed over JMX


1.1
===

Upgrading
---------
    - Compression is enabled by default on newly created ColumnFamilies
      (and unchanged for ColumnFamilies created prior to upgrading).
    - If you are running a multi datacenter setup, you should upgrade to
      the latest 1.0.x (or 0.8.x) release before upgrading.  Versions
      0.8.8 and 1.0.3-1.0.5 generate cross-dc forwarding that is incompatible
      with 1.1.
    - EACH_QUORUM ConsistencyLevel is only supported for writes and will now
      throw an InvalidRequestException when used for reads.  (Previous
      versions would silently perform a LOCAL_QUORUM read instead.)
    - ANY ConsistencyLevel is only supported for writes and will now
      throw an InvalidRequestException when used for reads.  (Previous
      versions would silently perform a ONE read for range queries;
      single-row and multiget reads already rejected ANY.)
    - The largest mutation batch accepted by the commitlog is now 128MB.
      (In practice, batches larger than ~10MB always caused poor
      performance due to load volatility and GC promotion failures.)
      Larger batches will continue to be accepted but will not be
      durable.  Consider setting durable_writes=false if you really
      want to use such large batches.
    - Make sure that global settings: key_cache_{size_in_mb, save_period}
      and row_cache_{size_in_mb, save_period} in conf/cassandra.yaml are
      used instead of per-ColumnFamily options.
    - JMX methods no longer return custom Cassandra objects.  Any such methods
      will now return standard Maps, Lists, etc.
    - Hadoop input and output details are now separated.  If you were
      previously using methods such as getRpcPort you now need to use
      getInputRpcPort or getOutputRpcPort depending on the circumstance.
    - CQL changes:
      + Prior to 1.1, you could use KEY as the primary key name in some
        select statements, even if the PK was actually given a different
        name.  In 1.1+ you must use the defined PK name.
    - The sliced_buffer_size_in_kb option has been removed from the
      cassandra.yaml config file (this option was a no-op since 1.0).

Features
--------
    - Concurrent schema updates are now supported, with any conflicts
      automatically resolved. Please note that simultaneously running
      ‘CREATE COLUMN FAMILY’ operation on the different nodes wouldn’t
      be safe until version 1.2 due to the nature of ColumnFamily
      identifier generation, for more details see CASSANDRA-3794.
    - The CQL language has undergone a major revision, CQL3, the
      highlights of which are covered at [1].  CQL3 is not
      backwards-compatibile with CQL2, so we've introduced a
      set_cql_version Thrift method to specify which version you want.
      (The default remains CQL2 at least until Cassandra 1.2.)  cqlsh
      adds a --cql3 flag to enable this.
      [1] http://www.datastax.com/dev/blog/schema-in-cassandra-1-1
    - Row-level isolation: multi-column updates to a single row have
      always been *atomic* (either all will be applied, or none)
      thanks to the CommitLog, but until 1.1 they were not *isolated*
      -- a reader may see mixed old and new values while the update
      happens.
    - Finer-grained control over data directories, allowing a ColumnFamily to
      be pinned to specfic volume, e.g. one backed by SSD.
    - The bulk loader is not longer a fat client; it can be run from an
      existing machine in a cluster.
    - A new write survey mode has been added, similar to bootstrap (enabled via
      -Dcassandra.write_survey=true), but the node will not automatically join
      the cluster.  This is useful for cases such as testing different
      compaction strategies with live traffic without affecting the cluster.
    - Key and row caches are now global, similar to the global memtable
      threshold. Manual tuning of cache sizes per-columnfamily is no longer
      required.
    - Off-heap caches no longer require JNA, and will work out of the box
      on Windows as well as Unix platforms.
    - Streaming is now multithreaded.
    - Compactions may now be aborted via JMX or nodetool.
    - The stress tool is not new in 1.1, but it is newly included in
      binary builds as well as the source tree
    - Hadoop: a new BulkOutputFormat is included which will directly write
      SSTables locally and then stream them into the cluster.
      YOU SHOULD USE BulkOutputFormat BY DEFAULT.  ColumnFamilyOutputFormat
      is still around in case for some strange reason you want results
      trickling out over Thrift, but BulkOutputFormat is significantly
      more efficient.
    - Hadoop: KeyRange.filter is now supported with ColumnFamilyInputFormat,
      allowing index expressions to be evaluated server-side to reduce
      the amount of data sent to Hadoop.
    - Hadoop: ColumnFamilyRecordReader has a wide-row mode, enabled via
      a boolean parameter to setInputColumnFamily, that pages through
      data column-at-a-time instead of row-at-a-time.
    - Pig: can use the wide-row Hadoop support, by setting PIG_WIDEROW_INPUT
      to true.  This will produce each row's columns in a bag.


1.0.8
=====

Upgrading
---------
    - Nothing specific to 1.0.8

Other
-----
    - Allow configuring socket timeout for streaming


1.0.7
=====

Upgrading
---------
    - Nothing specific to 1.0.7, please report to instruction for 1.0.6

Other
-----
    - Adds new setstreamthroughput to nodetool to configure streaming
      throttling
    - Adds JMX property to get/set rpc_timeout_in_ms at runtime
    - Allow configuring (per-CF) bloom_filter_fp_chance


1.0.6
=====

Upgrading
---------
    - This release fixes an issue related to the chunk_length_kb option for
      compressed sstables. If you use compression on some column families, it
      is recommended after the upgrade to check the value for this option on
      these column families (the default value is 64). In case the option would
      not be set correctly, you should update the column family definition,
      setting the right value and then run scrub on the column family.
    - Please report to instruction for 1.0.5 if coming from an older version.


1.0.5
=====

Upgrading
---------
    - 1.0.5 comes to fix two important regression of 1.0.4. So all information
      concerning 1.0.4 are valid for this release, but please avoids upgrading
      to 1.0.4.


1.0.4
=====

Upgrading
---------
    - Nothing specific to 1.0.4 but please see the 1.0 upgrading section if
      upgrading from a version prior to 1.0.0

Features
--------
    - A new upgradesstables command has been added to nodetool. It is very
      similar to scrub but without the ability to discard corrupted rows (and
      as a consequence it does not snapshot automatically before). This new
      command is to be prefered to scrub in all cases where sstables should be
      rewritten to the current format for upgrade purposes.

JMX
---
    - The path for the data, commit log and saved cache directories exposed
      through JMX
    - The in-memory bloom filter sizes are now exposed through JMX


1.0.3
=====

Upgrading
---------
    - Nothing specific to 1.0.3 but please see the 1.0 upgrading section if
      upgrading from a version prior to 1.0.0

Features
--------
    - For non compressed sstables (compressed sstable already include more
      fine grained checsums), a sha1 for the full sstable is now automatically
      created (in a fix with suffix -Digest.sha1). It can be used to check the
      sstable integrity with sha1sum.


1.0.2
=====

Upgrading
---------
    - Nothing specific to 1.0.2 but please see the 1.0 upgrading section if
      upgrading from a version prior to 1.0.0

Features
--------
    - Cassandra CLI queries now have timing information


1.0.1
=====

Upgrading
---------
    - If upgrading from a version prior to 1.0.0, please see the 1.0 Upgrading
      section
    - For running on Windows as a Service, procrun is no longer discributed
      with Cassandra, see README.txt for more information on how to download
      it if necessary.
    - The name given to snapshots directories have been improved for human
      readability. If you had scripts relying on it, you may need to update
      them.


1.0
===

Upgrading
---------
    - Upgrading from version 0.7.1+ or 0.8.2+ can be done with a rolling
      restart, one node at a time.  (0.8.0 or 0.8.1 are NOT network-compatible
      with 1.0: upgrade to the most recent 0.8 release first.)
      You do not need to bring down the whole cluster at once.
    - After upgrading, run nodetool scrub against each node before running
      repair, moving nodes, or adding new ones.
    - CQL inserts/updates now generate microsecond resolution timestamps
      by default, instead of millisecond. THIS MEANS A ROLLING UPGRADE COULD
      MIX milliseconds and microseconds, with clients talking to servers
      generating milliseconds unable to overwrite the larger microsecond
      timestamps. If you are using CQL and this is important for your
      application, you can either perform a non-rolling upgrade to 1.0, or
      update your application first to use explicit timestamps with the "USING
      timestamp=X" syntax.
    - The BinaryMemtable bulk-load interface has been removed (use the
      sstableloader tool instead).
    - The compaction_thread_priority setting has been removed from
      cassandra.yaml (use compaction_throughput_mb_per_sec to throttle
      compaction instead).
    - CQL types bytea and date were renamed to blob and timestamp, respectively,
      to conform with SQL norms.  CQL type int is now a 4-byte int, not 8
      (which is still available as bigint).
    - Cassandra 1.0 uses arena allocation to reduce old generation
      fragmentation.  This means there is a minimum overhead of 1MB
      per ColumnFamily plus 1MB per index.
    - The SimpleAuthenticator and SimpleAuthority classes have been moved to
      the example directory (and are thus not available from the binary
      distribution). They never provided actual security and in their current
      state are only meant as examples.

Features
--------
    - SSTable compression is supported through the 'compression_options'
      parameter when creating/updating a column family. For instance, you can
      create a column family Cf using compression (through the Snappy library)
      in the CLI with:
        create column family Cf with compression_options={sstable_compression: SnappyCompressor}
      SSTable compression is not activated by default but can be activated or
      deactivated at any time.
    - Compressed SSTable blocks are checksummed to protect against bitrot
    - New LevelDB-inspired compaction algorithm can be enabled by setting the
      Columnfamily compaction_strategy=LeveledCompactionStrategy option.
      Leveled compaction means you only need to keep a few MB of space free for
      compaction instead of (in the worst case) 50%.
    - Ability to use multiple threads during a single compaction. See
      multithreaded_compaction in cassandra.yaml for more details.
    - Windows Service ("cassandra.bat install" to enable)
    - A dead node may be replaced in a single step by starting a new node
      with -Dcassandra.replace_token=<token>. More details can be found at
      http://wiki.apache.org/cassandra/Operations#Replacing_a_Dead_Node
    - It is now possible to repair only the first range returned by the
      partitioner for a node with `nodetool repair -pr`. It makes it
      easier/possible to repair a full cluster without any work duplication by
      running this command on every node of the cluster.

New data types
--------------
    - decimal

Other
-----
    - Hinted Handoff has two major improvements:
        - Hint replay is much more efficient thanks to a change in the data model
        - Hints are created for all replicas that do not ack a write.  (Formerly,
          only replicas known to be down when the write started were hinted.)
      This means that running with read repair completely off is much more
      viable than before, and the default read_repair_chance is reduced from 1.0
      ("always repair") to 0.1 ("repair 10% of the time").
    - The old per-ColumnFamily memtable thresholds
      (memtable_throughput_in_mb, memtable_operations_in_millions,
      memtable_flush_after_mins) are ignored, in favor of the global
      memtable_total_space_in_mb and commitlog_total_space_in_mb settings.
      This does not affect client compatibility -- the old options are
      still allowed, but have no effect. These options may be removed
      entirely in a future release.
    - Backlogged compactions will begin five minutes after startup.  The 0.8
      behavior of never starting compaction until a flush happens is usually
      not what is desired, but a short grace period is useful to allow caches
      to warm up first.
    - The deletion of compacted data files is not performed during Garbage
      Collection anymore. This means compacted files will now be deleted
      without delay.


0.8.5
=====

Features
--------
    - SSTables copied to a data directory can be loaded by a live node through
      nodetool refresh (may be handy to load snapshots).
    - The configured compaction throughput is exposed through JMX.

Other
-----
    - The sstableloader is now bundled with the debian package.
    - Repair detects when a participating node is dead and fails instead of
      hanging forever.


0.8.4
=====

Upgrading
---------
    - Nothing specific to 0.8.4

Other
-----
    - This release comes to fix a bug in counter that could lead to
      (important) over-count.
    - It also fixes a slight upgrade regression from 0.8.3. It is thus advised
      to jump directly to 0.8.4 if upgrading from before 0.8.3.


0.8.3
=====

Upgrading
---------
    - Token removal has been revamped.  Removing tokens in a mixed cluster with
      0.8.3 will not work, so the entire cluster will need to be running 0.8.3
      first, except for the dead node.

Features
--------
    - It is now possible to use thrift asynchronous and
      half-synchronous/half-asynchronous servers (see cassandra.yaml for more
      details).
    - It is now possible to access counter columns through Hadoop.

Other
-----
    - This release fix a regression of 0.8 that can make commit log segment to
      be deleted even though not all data it contains has been flushed.
      Upgrades from 0.8.* is very much encouraged.


0.8.2
=====

Upgrading
---------
    - 0.8.0 and 0.8.1 shipped with a bug that was setting the
      replicate_on_write option for counter column families to false (this
      option has no effect on non-counter column family). This is an unsafe
      default and 0.8.2 correct this, the default for replicate_on_write is
      now true. It is advised to update your counter column family definitions
      if replicate_on_write was uncorrectly set to false (before or after
      upgrade).


0.8.1
=====

Upgrading
---------
    - 0.8.1 is backwards compatible with 0.8, upgrade can be achieved by a
      simple rolling restart.
    - If upgrading for earlier version (0.7), please refer to the 0.8 section
      for instructions.

Features
--------
    - Numerous additions/improvements to CQL (support for counters, TTL, batch
      inserts/deletes, index dropping, ...).
    - Add two new AbstractTypes (comparator) to support compound keys
      (CompositeType and DynamicCompositeType), as well as a ReverseType to
      reverse the order of any existing comparator.
    - New option to bypass the commit log on some keyspaces (for advanced
      users).

Tools
-----
    - Add new data bulk loading utility (sstableloader).


0.8
===

Upgrading
---------
    - Upgrading from version 0.7.1 or later can be done with a rolling
      restart, one node at a time.  You do not need to bring down the
      whole cluster at once.
    - After upgrading, run nodetool scrub against each node before running
      repair, moving nodes, or adding new ones.
    - Running nodetool drain before shutting down the 0.7 node is
      recommended but not required. (Skipping this will result in
      replay of entire commitlog, so it will take longer to restart but
      is otherwise harmless.)
    - 0.8 is fully API-compatible with 0.7.  You can continue
      to use your 0.7 clients.
    - Avro record classes used in map/reduce and Hadoop streaming code have
      been removed. Map/reduce can be switched to Thrift by changing
      org.apache.cassandra.avro in import statements to
      org.apache.cassandra.thrift (no class names change). Streaming support
      has been removed for the time being.
    - The loadbalance command has been removed from nodetool.  For similar
      behavior, decommission then rebootstrap with empty initial_token.
    - Thrift unframed mode has been removed.
    - The addition of key_validation_class means the cli will assume keys
      are bytes, instead of strings, in the absence of other information.
      See http://wiki.apache.org/cassandra/FAQ#cli_keys for more details.


Features
--------
    - added CQL client API and JDBC/DBAPI2-compliant drivers for Java and
      Python, respectively (see: drivers/ subdirectory and doc/cql)
    - added distributed Counters feature;
      see http://wiki.apache.org/cassandra/Counters
    - optional intranode encryption; see comments around 'encryption_options'
      in cassandra.yaml
    - compaction multithreading and rate-limiting; see
      'concurrent_compactors' and 'compaction_throughput_mb_per_sec' in
      cassandra.yaml
    - cassandra will limit total memtable memory usage to 1/3 of the heap
      by default.  This can be ajusted or disabled with the
      memtable_total_space_in_mb option.  The old per-ColumnFamily
      throughput, operations, and age settings are still respected but
      will be removed in a future major release once we are satisfied that
      memtable_total_space_in_mb works adequately.

Tools
-----
    - stress and py_stress moved from contrib/ to tools/
    - clustertool was removed (see
      https://issues.apache.org/jira/browse/CASSANDRA-2607 for examples
      of how to script nodetool across the cluster instead)

Other
-----
    - In the past, sstable2json would write column names and values as
      hex strings, and now creates human readable values based on the
      comparator/validator.  As a result, JSON dumps created with
      older versions of sstable2json are no longer compatible with
      json2sstable, and imports must be made with a configuration that
      is identical to the export.
    - manually-forced compactions ("nodetool compact") will do nothing
      if only a single SSTable remains for a ColumnFamily. To force it
      to compact that anyway (which will free up space if there are
      a lot of expired tombstones), use the new forceUserDefinedCompaction
      JMX method on CompactionManager.
    - most of contrib/ (which was not part of the binary releases)
      has been moved either to examples/ or tools/. We plan to move the
      rest for 0.8.1.

JMX
---
    - By default, JMX now listens on port 7199.


0.7.6
=====

Upgrading
---------
    - Nothing specific to 0.7.6, but see 0.7.3 Upgrading if upgrading
      from earlier than 0.7.1.


0.7.5
=====

Upgrading
---------
    - Nothing specific to 0.7.5, but see 0.7.3 Upgrading if upgrading
      from earlier than 0.7.1.

Changes
-------
    - system_update_column_family no longer snapshots before applying
      the schema change. (_update_keyspace never did.  _drop_keyspace
      and _drop_column_family continue to snapshot.)
    - added memtable_flush_queue_size option to cassandra.yaml to
      avoid blocking writes when multiple column families (or a colum
      family with indexes) are flushed at the same time.
    - allow overriding initial_token, storage_port and rpc_port using
      system properties


0.7.4
=====

Upgrading
---------
    - Nothing specific to 0.7.4, but see 0.7.3 Upgrading if upgrading
      from earlier than 0.7.1.

Features
--------
    - Output to Pig is now supported as well as input


0.7.3
=====

Upgrading
---------
    - 0.7.1 and 0.7.2 shipped with a bug that caused incorrect row-level
      bloom filters to be generated when compacting sstables generated
      with earlier versions.  This would manifest in IOExceptions during
      column name-based queries.  0.7.3 provides "nodetool scrub" to
      rebuild sstables with correct bloom filters, with no data lost.
      (If your cluster was never on 0.7.0 or earlier, you don't have to
      worry about this.)  Note that nodetool scrub will snapshot your
      data files before rebuilding, just in case.


0.7.1
=====

Upgrading
---------
    - 0.7.1 is completely backwards compatible with 0.7.0.  Just restart
      each node with the new version, one at a time.  (The cluster does
      not all need to be upgraded simultaneously.)

Features
--------
    - added flush_largest_memtables_at and reduce_cache_sizes_at options
      to cassandra.yaml as an escape valve for memory pressure
    - added option to specify -Dcassandra.join_ring=false on startup
      to allow "warm spare" nodes or performing JMX maintenance before
      joining the ring

Performance
-----------
    - Disk writes and sequential scans avoid polluting page cache
      (requires JNA to be enabled)
    - Cassandra performs writes efficiently across datacenters by
      sending a single copy of the mutation and having the recipient
      forward that to other replicas in its datacenter.
    - Improved network buffering
    - Reduced lock contention on memtable flush
    - Optimized supercolumn deserialization
    - Zero-copy reads from mmapped sstable files
    - Explicitly set higher JVM new generation size
    - Reduced i/o contention during saving of caches


0.7.0
=====

Features
--------
    - Secondary indexes (indexes on column values) are now supported
    - Row size limit increased from 2GB to 2 billion columns.  rows
      are no longer read into memory during compaction.
    - Keyspace and ColumnFamily definitions may be added and modified live
    - Streaming data for repair or node movement no longer requires
      anticompaction step first
    - NetworkTopologyStrategy (formerly DatacenterShardStrategy) is ready for
      use, enabling ConsistencyLevel.DCQUORUM and DCQUORUMSYNC.  See comments
      in `cassandra.yaml.`
    - Optional per-Column time-to-live field allows expiring data without
      have to issue explicit remove commands
    - `truncate` thrift method allows clearing an entire ColumnFamily at once
    - Hadoop OutputFormat and Streaming [non-jvm map/reduce via stdin/out]
      support
    - Up to 8x faster reads from row cache
    - A new ByteOrderedPartitioner supports bytes keys with arbitrary content,
      and orders keys by their byte value.  This should be used in new
      deployments instead of OrderPreservingPartitioner.
    - Optional round-robin scheduling between keyspaces for multitenant
      clusters
    - Dynamic endpoint snitch mitigates the impact of impaired nodes
    - New `IntegerType`, faster than LongType and allows integers of
      both less and more bits than Long's 64
    - A revamped authentication system that decouples authorization and
      allows finer-grained control of resources.

Upgrading
---------
    The Thrift API has changed in incompatible ways; see below, and refer
    to http://wiki.apache.org/cassandra/ClientOptions for a list of
    higher-level clients that have been updated to support the 0.7 API.

    The Cassandra inter-node protocol is incompatible with 0.6.x
    releases (and with 0.7 beta1), meaning you will have to bring your
    cluster down prior to upgrading: you cannot mix 0.6 and 0.7 nodes.

    The hints schema was changed from 0.6 to 0.7. Cassandra automatically
    snapshots and then truncates the hints column family as part of
    starting up 0.7 for the first time.

    Keyspace and ColumnFamily definitions are stored in the system
    keyspace, rather than the configuration file.

    The process to upgrade is:
    1) run "nodetool drain" on _each_ 0.6 node.  When drain finishes (log
       message "Node is drained" appears), stop the process.
    2) Convert your storage-conf.xml to the new cassandra.yaml using
       "bin/config-converter".
    3) Rename any of your keyspace or column family names that do not adhere
       to the '^\w+' regex convention.
    4) Start up your cluster with the 0.7 version.
    5) Initialize your Keyspace and ColumnFamily definitions using
       "bin/schematool <host> <jmxport> import".  _You only need to do
       this to one node_.

Thrift API
----------
    - The Cassandra server now defaults to framed mode, rather than
      unframed.  Unframed is obsolete and will be removed in the next
      major release.
    - The Cassandra Thrift interface file has been updated for Thrift 0.5.
      If you are compiling your own client code from the interface, you
      will need to upgrade the Thrift compiler to match.
    - Row keys are now bytes: keys stored by versions prior to 0.7.0 will be
      returned as UTF-8 encoded bytes. OrderPreservingPartitioner and
      CollatingOrderPreservingPartitioner continue to expect that keys contain
      UTF-8 encoded strings, but RandomPartitioner now works on any key data.
    - keyspace parameters have been replaced with the per-connection
      set_keyspace method.
    - The return type for login() is now AccessLevel.
    - The get_string_property() method has been removed.
    - The get_string_list_property() method has been removed.

Configuraton
------------
    - Configuration file renamed to cassandra.yaml and log4j.properties to
      log4j-server.properties
    - PropertyFileSnitch configuration file renamed to
      cassandra-topology.properties
    - The ThriftAddress and ThriftPort directives have been renamed to
      RPCAddress and RPCPort respectively.
    - EndPointSnitch was renamed to RackInferringSnitch.  A new SimpleSnitch
      has been added.
    - RackUnawareStrategy and RackAwareStrategy have been renamed to
      SimpleStrategy and OldNetworkTopologyStrategy, respectively.
    - RowWarningThresholdInMB replaced with in_memory_compaction_limit_in_mb
    - GCGraceSeconds is now per-ColumnFamily instead of global
	- Keyspace and column family names that do not confirm to a '^\w+' regex
      are considered illegal.
    - Keyspace and column family definitions will need to be loaded via
      "bin/schematool <host> <jmxport> import".  _You only need to do this to
      one node_.
    - In addition to an authenticator, an authority must be configured as
      well. Users of SimpleAuthenticator should use SimpleAuthority for this
      value (the default is AllowAllAuthority, which corresponds with
      AllowAllAuthenticator).
    - The format of access.properties has changed, see the sample configuration
      conf/access.properties for documentation on the new format.


JMX
---
    - StreamingService moved from o.a.c.streaming to o.a.c.service
    - GMFD renamed to GOSSIP_STAGE
    - {Min,Mean,Max}RowCompactedSize renamed to {Min,Mean,Max}RowSize
      since it no longer has to wait til compaction to be computed

Other
-----
    - If extending AbstractType, make sure you follow the singleton pattern
      followed by Cassandra core AbstractType classes: provide a public
      static final variable called 'instance'.


0.6.6
=====

Upgrading
---------
    - As part of the cache-saving feature, a third directory
      (along with data and commitlog) has been added to the config
      file.  You will need to set and create this directory
      when restarting your node into 0.6.6.


0.6.1
=====

Upgrading
---------
    - We try to keep minor versions 100% compatible (data format,
      commitlog format, network format) within the major series, but
      we introduced a network-level incompatibility in 0.6.1.
      Thus, if you are upgrading from 0.6.0 to any higher version
      (0.6.1, 0.6.2, etc.) then you will need to restart your entire
      cluster with the new version, instead of being able to do a
      rolling restart.


0.6.0
=====

Features
--------
    - row caching: configure with the RowsCached attribute in
      ColumnFamily definition
    - Hadoop map/reduce support: see contrib/word_count for an example
    - experimental authentication support, described under
      Authenticator in storage.conf

Configuraton
------------
    - MemtableSizeInMB has been replaced by MemtableThroughputInMB which
      triggers a memtable flush when the specified amount of data has
      been written, including overwrites.
    - MemtableObjectCountInMillions has been replaced by the
      MemtableOperationsInMillions directive which causes a memtable flush
      to occur after the specified number of operations.
    - Like MemtableSizeInMB, BinaryMemtableSizeInMB has been replaced by
      BinaryMemtableThroughputInMB.
    - Replication factor is now per-keyspace, rather than global.
    - KeysCachedFraction is deprecated in favor of KeysCached
    - RowWarningThresholdInMB added, to warn before very large rows
      get big enough to threaten node stability

Thrift API
----------
    - removed deprecated get_key_range method
    - added batch_mutate meethod
    - deprecated multiget and batch_insert methods in favor of
      multiget_slice and batch_mutate, respectively
    - added ConsistencyLevel.ANY, for when you want write
      availability even when it may not be readable immediately.
      Unlike CL.ZERO, though, it will throw an exception if
      it cannot be written *somewhere*.

JMX metrics
-----------
    - read and write statistics are reported as lifetime totals,
      instead of averages over the last minute.  average-since-last
      requested are also available for convenience.
    - cache hit rate statistics are now available from JMX under
      org.apache.cassandra.db.Caches
    - compaction JMX metrics are moved to
      org.apache.cassandra.db.CompactionManager.  PendingTasks is now
      a much better estimate of compactions remaining, and the
      progress of the current compaction has been added.
    - commitlog JMX metrics are moved to org.apache.cassandra.db.Commitlog
    - progress of data streaming during bootstrap, loadbalance, or other
      data migration, is available under
      org.apache.cassandra.streaming.StreamingService.
      See http://wiki.apache.org/cassandra/Streaming for details.

Installation/Upgrade
--------------------
    - 0.6 network traffic is not compatible with earlier versions.  You
      will need to shut down all your nodes at once, upgrade, then restart.


0.5.0
=====

0. The commitlog format has changed (but sstable format has not).
   When upgrading from 0.4, empty the commitlog either by running
   bin/nodeprobe flush on each machine and waiting for the flush to finish,
   or simply remove the commitlog directory if you only have test data.
   (If more writes come in after the flush command, starting 0.5 will error
   out; if that happens, just go back to 0.4 and flush again.)
   The format changed twice: from 0.4 to beta1, and from beta2 to RC1.

.5 The gossip protocol has changed, meaning 0.5 nodes cannot coexist
   in a cluster of 0.4 nodes or vice versa; you must upgrade your
   whole cluster at the same time.

1. Bootstrap, move, load balancing, and active repair have been added.
   See http://wiki.apache.org/cassandra/Operations.  When upgrading
   from 0.4, leave autobootstrap set to false for the first restart
   of your old nodes.

2. Performance improvements across the board, especially on the write
   path (over 100% improvement in stress.py throughput).

3. Configuration:
     - Added "comment" field to ColumnFamily definition.
     - Added MemtableFlushAfterMinutes, a global replacement for the
       old per-CF FlushPeriodInMinutes setting
     - Key cache settings

4. Thrift:
     - Added get_range_slice, deprecating get_key_range


0.4.2
=====

1. Improve default garbage collector options significantly --
   throughput will be 30% higher or more.


0.4.1
=====

1. SnapshotBeforeCompaction configuration option allows snapshotting
   before each compaction, which allows rolling back to any version
   of the data.


0.4.0
=====

1. On-disk data format has changed to allow billions of keys/rows per
   node instead of only millions.  The new format is incompatible with 0.3;
   see 0.3 notes below for how to import data from a 0.3 install.

2. Cassandra now supports multiple keyspaces.  Typically you will have
   one keyspace per application, allowing applications to be able to
   create and modify ColumnFamilies at will without worrying about
   collisions with others in the same cluster.

3. Many Thrift API changes and documentation.  See
   http://wiki.apache.org/cassandra/API

4. Removed the web interface in favor of JMX and bin/nodeprobe, which
   has significantly enhanced functionality.

5. Renamed configuration "<Table>" to "<Keyspace>".

6. Added commitlog fsync; see "<CommitLogSync>" in configuration.


0.3.0
=====

1. With enough and large enough keys in a ColumnFamily, Cassandra will
   run out of memory trying to perform compactions (data file merges).
   The size of what is stored in memory is (S + 16) * (N + M) where S
   is the size of the key (usually 2 bytes per character), N is the
   number of keys and M, is the map overhead (which can be guestimated
   at around 32 bytes per key).
   So, if you have 10-character keys and 1GB of headroom in your heap
   space for compaction, you can expect to store about 17M keys
   before running into problems.
   See https://issues.apache.org/jira/browse/CASSANDRA-208

2. Because fixing #1 requires a data file format change, 0.4 will not
   be binary-compatible with 0.3 data files.  A client-side upgrade
   can be done relatively easily with the following algorithm:
     for key in old_client.get_key_range(everything):
         columns = old_client.get_slice or get_slice_super(key, all columns)
     new_client.batch_insert or batch_insert_super(key, columns)
   The inner loop can be trivially parallelized for speed.

3. Commitlog does not fsync before reporting a write successful.
   Using blocking writes mitigates this to some degree, since all
   nodes that were part of the write quorum would have to fail
   before sync for data to be lost.
   See https://issues.apache.org/jira/browse/CASSANDRA-182

Additionally, row size (that is, all the data associated with a single
key in a given ColumnFamily) is limited by available memory, because
compaction deserializes each row before merging.

See https://issues.apache.org/jira/browse/CASSANDRA-16