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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!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 16.3 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> [, ...] ]
ANALYZE [ VERBOSE ] [ <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>
<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="53.51. 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><p>
When the option list is surrounded by parentheses, the options can be
written in any order. The parenthesized syntax was added in
<span class="productname">PostgreSQL</span> 11; the unparenthesized syntax
is deprecated.
</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.
</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 the specified table is a partitioned table, both the
inheritance statistics of the partitioned table as a whole and
statistics of the individual partitions are updated.
</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 be the table's owner or a
superuser. However, database owners are allowed to
analyze all tables in their databases, except shared catalogs.
(The restriction for shared catalogs means that a true database-wide
<code class="command">ANALYZE</code> can only be performed by a superuser.)
<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="25.1.6. The Autovacuum Daemon">Section 25.1.6</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>
<code class="command">ANALYZE</code>
requires only a read lock on the target table, so it can run in
parallel with other 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 25. Routine Database Maintenance Tasks">Chapter 25</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 child
tables themselves are not individually analyzed in this case.
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.
</p><p>
For partitioned tables, <code class="command">ANALYZE</code> gathers statistics by
sampling rows from all partitions; in addition, it will recurse into each
partition and update its statistics. Each leaf partition is analyzed only
once, even with multi-level partitioning. No statistics are collected for
only the parent table (without data from its partitions), because with
partitioning it's guaranteed to be empty.
</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="28.4.1. ANALYZE Progress Reporting">Section 28.4.1</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></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-resource.html#RUNTIME-CONFIG-RESOURCE-VACUUM-COST" title="20.4.4. Cost-based Vacuum Delay">Section 20.4.4</a>, <a class="xref" href="routine-vacuuming.html#AUTOVACUUM" title="25.1.6. The Autovacuum Daemon">Section 25.1.6</a>, <a class="xref" href="progress-reporting.html#ANALYZE-PROGRESS-REPORTING" title="28.4.1. ANALYZE Progress Reporting">Section 28.4.1</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 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> BEGIN</td></tr></table></div></body></html>
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