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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>ANALYZE</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-alterview.html" title="ALTER VIEW" /><link rel="next" href="sql-begin.html" title="BEGIN" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">ANALYZE</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-alterview.html" title="ALTER VIEW">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 18.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-begin.html" title="BEGIN">Next</a></td></tr></table><hr /></div><div class="refentry" id="SQL-ANALYZE"><div class="titlepage"></div><a id="id-1.9.3.46.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">ANALYZE</span></h2><p>ANALYZE — collect statistics about a database</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
ANALYZE [ ( <em class="replaceable"><code>option</code></em> [, ...] ) ] [ <em class="replaceable"><code>table_and_columns</code></em> [, ...] ]

<span class="phrase">where <em class="replaceable"><code>option</code></em> can be one of:</span>

    VERBOSE [ <em class="replaceable"><code>boolean</code></em> ]
    SKIP_LOCKED [ <em class="replaceable"><code>boolean</code></em> ]
    BUFFER_USAGE_LIMIT <em class="replaceable"><code>size</code></em>

<span class="phrase">and <em class="replaceable"><code>table_and_columns</code></em> is:</span>

    [ ONLY ] <em class="replaceable"><code>table_name</code></em> [ * ] [ ( <em class="replaceable"><code>column_name</code></em> [, ...] ) ]
</pre></div><div class="refsect1" id="id-1.9.3.46.5"><h2>Description</h2><p>
   <code class="command">ANALYZE</code> collects statistics about the contents
   of tables in the database, and stores the results in the <a class="link" href="catalog-pg-statistic.html" title="52.51. pg_statistic"><code class="structname">pg_statistic</code></a>
   system catalog.  Subsequently, the query planner uses these
   statistics to help determine the most efficient execution plans for
   queries.
  </p><p>
   Without a <em class="replaceable"><code>table_and_columns</code></em>
   list, <code class="command">ANALYZE</code> processes every table and materialized view
   in the current database that the current user has permission to analyze.
   With a list, <code class="command">ANALYZE</code> processes only those table(s).
   It is further possible to give a list of column names for a table,
   in which case only the statistics for those columns are collected.
  </p></div><div class="refsect1" id="id-1.9.3.46.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">VERBOSE</code></span></dt><dd><p>
      Enables display of progress messages at <code class="literal">INFO</code> level.
     </p></dd><dt><span class="term"><code class="literal">SKIP_LOCKED</code></span></dt><dd><p>
      Specifies that <code class="command">ANALYZE</code> should not wait for any
      conflicting locks to be released when beginning work on a relation:
      if a relation cannot be locked immediately without waiting, the relation
      is skipped.  Note that even with this option, <code class="command">ANALYZE</code>
      may still block when opening the relation's indexes or when acquiring
      sample rows from partitions, table inheritance children, and some
      types of foreign tables.  Also, while <code class="command">ANALYZE</code>
      ordinarily processes all partitions of specified partitioned tables,
      this option will cause <code class="command">ANALYZE</code> to skip all
      partitions if there is a conflicting lock on the partitioned table.
     </p></dd><dt><span class="term"><code class="literal">BUFFER_USAGE_LIMIT</code></span></dt><dd><p>
      Specifies the
      <a class="glossterm" href="glossary.html#GLOSSARY-BUFFER-ACCESS-STRATEGY"><em class="glossterm"><a class="glossterm" href="glossary.html#GLOSSARY-BUFFER-ACCESS-STRATEGY" title="Buffer Access Strategy">Buffer Access Strategy</a></em></a>
      ring buffer size for <code class="command">ANALYZE</code>.  This size is used to
      calculate the number of shared buffers which will be reused as part of
      this strategy.  <code class="literal">0</code> disables use of a
      <code class="literal">Buffer Access Strategy</code>.   When this option is not
      specified, <code class="command">ANALYZE</code> uses the value from
      <a class="xref" href="runtime-config-resource.html#GUC-VACUUM-BUFFER-USAGE-LIMIT">vacuum_buffer_usage_limit</a>.  Higher settings can
      allow <code class="command">ANALYZE</code> to run more quickly, but having too
      large a setting may cause too many other useful pages to be evicted from
      shared buffers.  The minimum value is <code class="literal">128 kB</code> and the
      maximum value is <code class="literal">16 GB</code>.
     </p></dd><dt><span class="term"><em class="replaceable"><code>boolean</code></em></span></dt><dd><p>
      Specifies whether the selected option should be turned on or off.
      You can write <code class="literal">TRUE</code>, <code class="literal">ON</code>, or
      <code class="literal">1</code> to enable the option, and <code class="literal">FALSE</code>,
      <code class="literal">OFF</code>, or <code class="literal">0</code> to disable it.  The
      <em class="replaceable"><code>boolean</code></em> value can also
      be omitted, in which case <code class="literal">TRUE</code> is assumed.
     </p></dd><dt><span class="term"><em class="replaceable"><code>size</code></em></span></dt><dd><p>
      Specifies an amount of memory in kilobytes.  Sizes may also be specified
      as a string containing the numerical size followed by any one of the
      following memory units: <code class="literal">B</code> (bytes),
      <code class="literal">kB</code> (kilobytes), <code class="literal">MB</code> (megabytes),
      <code class="literal">GB</code> (gigabytes), or <code class="literal">TB</code> (terabytes).
     </p></dd><dt><span class="term"><em class="replaceable"><code>table_name</code></em></span></dt><dd><p>
      The name (possibly schema-qualified) of a specific table to
      analyze.  If omitted, all regular tables, partitioned tables, and
      materialized views in the current database are analyzed (but not
      foreign tables).  If <code class="literal">ONLY</code> is specified before
      the table name, only that table is analyzed.  If <code class="literal">ONLY</code>
      is not specified, the table and all its inheritance child tables or
      partitions (if any) are analyzed.  Optionally, <code class="literal">*</code>
      can be specified after the table name to explicitly indicate that
      inheritance child tables (or partitions) are to be analyzed.
     </p></dd><dt><span class="term"><em class="replaceable"><code>column_name</code></em></span></dt><dd><p>
      The name of a specific column to analyze. Defaults to all columns.
     </p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.46.7"><h2>Outputs</h2><p>
    When <code class="literal">VERBOSE</code> is specified, <code class="command">ANALYZE</code> emits
    progress messages to indicate which table is currently being
    processed.  Various statistics about the tables are printed as well.
   </p></div><div class="refsect1" id="id-1.9.3.46.8"><h2>Notes</h2><p>
   To analyze a table, one must ordinarily have the <code class="literal">MAINTAIN</code>
   privilege on the table.  However, database owners are allowed to
   analyze all tables in their databases, except shared catalogs.
   <code class="command">ANALYZE</code> will skip over any tables that the calling user
   does not have permission to analyze.
  </p><p>
   Foreign tables are analyzed only when explicitly selected.  Not all
   foreign data wrappers support <code class="command">ANALYZE</code>.  If the table's
   wrapper does not support <code class="command">ANALYZE</code>, the command prints a
   warning and does nothing.
  </p><p>
   In the default <span class="productname">PostgreSQL</span> configuration,
   the autovacuum daemon (see <a class="xref" href="routine-vacuuming.html#AUTOVACUUM" title="24.1.6. The Autovacuum Daemon">Section 24.1.6</a>)
   takes care of automatic analyzing of tables when they are first loaded
   with data, and as they change throughout regular operation.
   When autovacuum is disabled,
   it is a good idea to run <code class="command">ANALYZE</code> periodically, or
   just after making major changes in the contents of a table.  Accurate
   statistics will help the planner to choose the most appropriate query
   plan, and thereby improve the speed of query processing.  A common
   strategy for read-mostly databases is to run <a class="link" href="sql-vacuum.html" title="VACUUM"><code class="command">VACUUM</code></a>
   and <code class="command">ANALYZE</code> once a day during a low-usage time of day.
   (This will not be sufficient if there is heavy update activity.)
  </p><p>
   While <code class="command">ANALYZE</code> is running, the <a class="xref" href="runtime-config-client.html#GUC-SEARCH-PATH">search_path</a> is temporarily changed to <code class="literal">pg_catalog,
   pg_temp</code>.
  </p><p>
   <code class="command">ANALYZE</code>
   requires only a read lock on the target table, so it can run in
   parallel with other non-DDL activity on the table.
  </p><p>
   The statistics collected by <code class="command">ANALYZE</code> usually
   include a list of some of the most common values in each column and
   a histogram showing the approximate data distribution in each
   column.  One or both of these can be omitted if
   <code class="command">ANALYZE</code> deems them uninteresting (for example,
   in a unique-key column, there are no common values) or if the
   column data type does not support the appropriate operators.  There
   is more information about the statistics in <a class="xref" href="maintenance.html" title="Chapter 24. Routine Database Maintenance Tasks">Chapter 24</a>.
  </p><p>
   For large tables, <code class="command">ANALYZE</code> takes a random sample
   of the table contents, rather than examining every row.  This
   allows even very large tables to be analyzed in a small amount of
   time.  Note, however, that the statistics are only approximate, and
   will change slightly each time <code class="command">ANALYZE</code> is run,
   even if the actual table contents did not change.  This might result
   in small changes in the planner's estimated costs shown by
   <a class="link" href="sql-explain.html" title="EXPLAIN"><code class="command">EXPLAIN</code></a>.
   In rare situations, this non-determinism will cause the planner's
   choices of query plans to change after <code class="command">ANALYZE</code> is run.
   To avoid this, raise the amount of statistics collected by
   <code class="command">ANALYZE</code>, as described below.
  </p><p>
   The extent of analysis can be controlled by adjusting the
   <a class="xref" href="runtime-config-query.html#GUC-DEFAULT-STATISTICS-TARGET">default_statistics_target</a> configuration variable, or
   on a column-by-column basis by setting the per-column statistics
   target with <a class="link" href="sql-altertable.html" title="ALTER TABLE"><code class="command">ALTER TABLE ... ALTER COLUMN ... SET
   STATISTICS</code></a>.
   The target value sets the
   maximum number of entries in the most-common-value list and the
   maximum number of bins in the histogram.  The default target value
   is 100, but this can be adjusted up or down to trade off accuracy of
   planner estimates against the time taken for
   <code class="command">ANALYZE</code> and the amount of space occupied in
   <code class="literal">pg_statistic</code>.  In particular, setting the
   statistics target to zero disables collection of statistics for
   that column.  It might be useful to do that for columns that are
   never used as part of the <code class="literal">WHERE</code>, <code class="literal">GROUP BY</code>,
   or <code class="literal">ORDER BY</code> clauses of queries, since the planner will
   have no use for statistics on such columns.
  </p><p>
   The largest statistics target among the columns being analyzed determines
   the number of table rows sampled to prepare the statistics.  Increasing
   the target causes a proportional increase in the time and space needed
   to do <code class="command">ANALYZE</code>.
  </p><p>
   One of the values estimated by <code class="command">ANALYZE</code> is the number of
   distinct values that appear in each column.  Because only a subset of the
   rows are examined, this estimate can sometimes be quite inaccurate, even
   with the largest possible statistics target.  If this inaccuracy leads to
   bad query plans, a more accurate value can be determined manually and then
   installed with
   <a class="link" href="sql-altertable.html" title="ALTER TABLE"><code class="command">ALTER TABLE ... ALTER COLUMN ... SET (n_distinct = ...)</code></a>.
  </p><p>
    If the table being analyzed has inheritance children,
    <code class="command">ANALYZE</code> gathers two sets of statistics: one on the rows
    of the parent table only, and a second including rows of both the parent
    table and all of its children.  This second set of statistics is needed when
    planning queries that process the inheritance tree as a whole.  The
    autovacuum daemon, however, will only consider inserts or updates on the
    parent table itself when deciding whether to trigger an automatic analyze
    for that table.  If that table is rarely inserted into or updated, the
    inheritance statistics will not be up to date unless you run
    <code class="command">ANALYZE</code> manually.  By default,
    <code class="command">ANALYZE</code> will also recursively collect and update the
    statistics for each inheritance child table.  The <code class="literal">ONLY</code>
    keyword may be used to disable this.
  </p><p>
    For partitioned tables, <code class="command">ANALYZE</code> gathers statistics by
    sampling rows from all partitions.  By default,
    <code class="command">ANALYZE</code> will also recursively collect and update the
    statistics for each partition.  The <code class="literal">ONLY</code> keyword may be
    used to disable this.
  </p><p>
    The autovacuum daemon does not process partitioned tables, nor does it
    process inheritance parents if only the children are ever modified.
    It is usually necessary to periodically run a manual
    <code class="command">ANALYZE</code> to keep the statistics of the table hierarchy
    up to date.
  </p><p>
    If any child tables or partitions are foreign tables whose foreign
    data wrappers do not support <code class="command">ANALYZE</code>, those tables are
    ignored while gathering inheritance statistics.
  </p><p>
    If the table being analyzed is completely empty, <code class="command">ANALYZE</code>
    will not record new statistics for that table.  Any existing statistics
    will be retained.
  </p><p>
    Each backend running <code class="command">ANALYZE</code> will report its progress
    in the <code class="structname">pg_stat_progress_analyze</code> view. See
    <a class="xref" href="progress-reporting.html#ANALYZE-PROGRESS-REPORTING" title="27.4.1. ANALYZE Progress Reporting">Section 27.4.1</a> for details.
  </p></div><div class="refsect1" id="id-1.9.3.46.9"><h2>Compatibility</h2><p>
   There is no <code class="command">ANALYZE</code> statement in the SQL standard.
  </p><p>
   The following syntax was used before <span class="productname">PostgreSQL</span>
   version 11 and is still supported:
</p><pre class="synopsis">
ANALYZE [ VERBOSE ] [ <em class="replaceable"><code>table_and_columns</code></em> [, ...] ]
</pre><p>
  </p></div><div class="refsect1" id="id-1.9.3.46.10"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-vacuum.html" title="VACUUM"><span class="refentrytitle">VACUUM</span></a>, <a class="xref" href="app-vacuumdb.html" title="vacuumdb"><span class="refentrytitle"><span class="application">vacuumdb</span></span></a>, <a class="xref" href="runtime-config-vacuum.html#RUNTIME-CONFIG-RESOURCE-VACUUM-COST" title="19.10.2. Cost-based Vacuum Delay">Section 19.10.2</a>, <a class="xref" href="routine-vacuuming.html#AUTOVACUUM" title="24.1.6. The Autovacuum Daemon">Section 24.1.6</a>, <a class="xref" href="progress-reporting.html#ANALYZE-PROGRESS-REPORTING" title="27.4.1. ANALYZE Progress Reporting">Section 27.4.1</a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-alterview.html" title="ALTER VIEW">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-begin.html" title="BEGIN">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ALTER VIEW </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 18.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> BEGIN</td></tr></table></div></body></html>