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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="parquet_read_statistics"> |
| |
| <title>PARQUET_READ_STATISTICS Query Option (<keyword keyref="impala29"/> or higher only)</title> |
| |
| <titlealts audience="PDF"> |
| |
| <navtitle>PARQUET_READ_STATISTICS</navtitle> |
| |
| </titlealts> |
| |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| <data name="Category" value="Parquet"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| The <codeph>PARQUET_READ_STATISTICS</codeph> query option controls whether to read |
| statistics from Parquet files and use them during query processing. |
| </p> |
| |
| <p> |
| Parquet stores min/max stats which can be used to skip reading row groups if they don't |
| qualify a certain predicate. When this query option is set to <codeph>true</codeph>, |
| Impala reads the Parquet statistics and skips reading row groups that do not match the |
| conditions in the <codeph>WHERE</codeph> clause. |
| </p> |
| |
| <p> |
| Impala supports filtering based on Parquet statistics: |
| </p> |
| |
| <ul> |
| <li> |
| Of the numerical types for the old version of the statistics: Boolean, Integer, Float |
| </li> |
| |
| <li> |
| Of the types for the new version of the statistics (starting in IMPALA 2.8): Boolean, |
| Integer, Float, Decimal, String, Timestamp |
| </li> |
| |
| <li> |
| For simple predicates of the forms: <codeph><slot> <op> <constant></codeph> or |
| <codeph><constant> <op> <slot></codeph>, where <codeph><op></codeph> is LT, |
| LE, GE, GT, and EQ |
| </li> |
| </ul> |
| |
| <p> |
| The <codeph>PARQUET_READ_STATISTICS</codeph> option provides a workaround when dealing |
| with files that have corrupt Parquet statistics and unknown errors. |
| </p> |
| |
| <p> |
| In the query runtime profile output for each Impalad instance, the |
| <codeph>NumStatsFilteredRowGroups</codeph> field in the SCAN node section shows the number |
| of row groups that were skipped based on Parquet statistics. |
| </p> |
| |
| <p> |
| The supported values for the query option are: |
| <ul> |
| <li> |
| <codeph>true</codeph> (<codeph>1</codeph>): Read statistics from Parquet files and use |
| them in query processing. |
| </li> |
| |
| <li> |
| <codeph>false</codeph> (<codeph>0</codeph>): Do not use Parquet read statistics. |
| </li> |
| |
| <li> |
| Any other values are treated as <codeph>false</codeph>. |
| </li> |
| </ul> |
| </p> |
| |
| <p> |
| <b>Type:</b> Boolean |
| </p> |
| |
| <p> |
| <b>Default:</b> <codeph>true</codeph> |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_290"/> |
| |
| </conbody> |
| |
| </concept> |