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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>F.29. pg_stat_statements</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 V1.79.1" /><link rel="prev" href="pgrowlocks.html" title="F.28. pgrowlocks" /><link rel="next" href="pgstattuple.html" title="F.30. pgstattuple" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.29. pg_stat_statements</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pgrowlocks.html" title="F.28. pgrowlocks">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgstattuple.html" title="F.30. pgstattuple">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PGSTATSTATEMENTS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.29. pg_stat_statements</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgstatstatements.html#id-1.11.7.38.6">F.29.1. The <code class="structname">pg_stat_statements</code> View</a></span></dt><dt><span class="sect2"><a href="pgstatstatements.html#id-1.11.7.38.7">F.29.2. Functions</a></span></dt><dt><span class="sect2"><a href="pgstatstatements.html#id-1.11.7.38.8">F.29.3. Configuration Parameters</a></span></dt><dt><span class="sect2"><a href="pgstatstatements.html#id-1.11.7.38.9">F.29.4. Sample Output</a></span></dt><dt><span class="sect2"><a href="pgstatstatements.html#id-1.11.7.38.10">F.29.5. Authors</a></span></dt></dl></div><a id="id-1.11.7.38.2" class="indexterm"></a><p>
  The <code class="filename">pg_stat_statements</code> module provides a means for
  tracking execution statistics of all SQL statements executed by a server.
 </p><p>
  The module must be loaded by adding <code class="literal">pg_stat_statements</code> to
  <a class="xref" href="runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES">shared_preload_libraries</a> in
  <code class="filename">postgresql.conf</code>, because it requires additional shared memory.
  This means that a server restart is needed to add or remove the module.
 </p><p>
   When <code class="filename">pg_stat_statements</code> is loaded, it tracks
   statistics across all databases of the server.  To access and manipulate
   these statistics, the module provides a view, <code class="structname">pg_stat_statements</code>,
   and the utility functions <code class="function">pg_stat_statements_reset</code> and
   <code class="function">pg_stat_statements</code>.  These are not available globally but
   can be enabled for a specific database with
   <code class="command">CREATE EXTENSION pg_stat_statements</code>.
 </p><div class="sect2" id="id-1.11.7.38.6"><div class="titlepage"><div><div><h3 class="title">F.29.1. The <code class="structname">pg_stat_statements</code> View</h3></div></div></div><p>
   The statistics gathered by the module are made available via a
   view named <code class="structname">pg_stat_statements</code>.  This view
   contains one row for each distinct database ID, user ID and query
   ID (up to the maximum number of distinct statements that the module
   can track).  The columns of the view are shown in
   <a class="xref" href="pgstatstatements.html#PGSTATSTATEMENTS-COLUMNS" title="Table F.21. pg_stat_statements Columns">Table F.21</a>.
  </p><div class="table" id="PGSTATSTATEMENTS-COLUMNS"><p class="title"><strong>Table F.21. <code class="structname">pg_stat_statements</code> Columns</strong></p><div class="table-contents"><table class="table" summary="pg_stat_statements Columns" border="1"><colgroup><col /><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Type</th><th>References</th><th>Description</th></tr></thead><tbody><tr><td><code class="structfield">userid</code></td><td><code class="type">oid</code></td><td><code class="literal"><a class="link" href="catalog-pg-authid.html" title="51.8. pg_authid"><code class="structname">pg_authid</code></a>.oid</code></td><td>OID of user who executed the statement</td></tr><tr><td><code class="structfield">dbid</code></td><td><code class="type">oid</code></td><td><code class="literal"><a class="link" href="catalog-pg-database.html" title="51.15. pg_database"><code class="structname">pg_database</code></a>.oid</code></td><td>OID of database in which the statement was executed</td></tr><tr><td><code class="structfield">queryid</code></td><td><code class="type">bigint</code></td><td> </td><td>Internal hash code, computed from the statement's parse tree</td></tr><tr><td><code class="structfield">query</code></td><td><code class="type">text</code></td><td> </td><td>Text of a representative statement</td></tr><tr><td><code class="structfield">calls</code></td><td><code class="type">bigint</code></td><td> </td><td>Number of times executed</td></tr><tr><td><code class="structfield">total_time</code></td><td><code class="type">double precision</code></td><td> </td><td>Total time spent in the statement, in milliseconds</td></tr><tr><td><code class="structfield">min_time</code></td><td><code class="type">double precision</code></td><td> </td><td>Minimum time spent in the statement, in milliseconds</td></tr><tr><td><code class="structfield">max_time</code></td><td><code class="type">double precision</code></td><td> </td><td>Maximum time spent in the statement, in milliseconds</td></tr><tr><td><code class="structfield">mean_time</code></td><td><code class="type">double precision</code></td><td> </td><td>Mean time spent in the statement, in milliseconds</td></tr><tr><td><code class="structfield">stddev_time</code></td><td><code class="type">double precision</code></td><td> </td><td>Population standard deviation of time spent in the statement, in milliseconds</td></tr><tr><td><code class="structfield">rows</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of rows retrieved or affected by the statement</td></tr><tr><td><code class="structfield">shared_blks_hit</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of shared block cache hits by the statement</td></tr><tr><td><code class="structfield">shared_blks_read</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of shared blocks read by the statement</td></tr><tr><td><code class="structfield">shared_blks_dirtied</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of shared blocks dirtied by the statement</td></tr><tr><td><code class="structfield">shared_blks_written</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of shared blocks written by the statement</td></tr><tr><td><code class="structfield">local_blks_hit</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of local block cache hits by the statement</td></tr><tr><td><code class="structfield">local_blks_read</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of local blocks read by the statement</td></tr><tr><td><code class="structfield">local_blks_dirtied</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of local blocks dirtied by the statement</td></tr><tr><td><code class="structfield">local_blks_written</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of local blocks written by the statement</td></tr><tr><td><code class="structfield">temp_blks_read</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of temp blocks read by the statement</td></tr><tr><td><code class="structfield">temp_blks_written</code></td><td><code class="type">bigint</code></td><td> </td><td>Total number of temp blocks written by the statement</td></tr><tr><td><code class="structfield">blk_read_time</code></td><td><code class="type">double precision</code></td><td> </td><td>
        Total time the statement spent reading blocks, in milliseconds
        (if <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-IO-TIMING">track_io_timing</a> is enabled, otherwise zero)
      </td></tr><tr><td><code class="structfield">blk_write_time</code></td><td><code class="type">double precision</code></td><td> </td><td>
        Total time the statement spent writing blocks, in milliseconds
        (if <a class="xref" href="runtime-config-statistics.html#GUC-TRACK-IO-TIMING">track_io_timing</a> is enabled, otherwise zero)
      </td></tr></tbody></table></div></div><br class="table-break" /><p>
   For security reasons, only superusers and members of the
   <code class="literal">pg_read_all_stats</code> role are allowed to see the SQL text and
   <code class="structfield">queryid</code> of queries executed by other users.
   Other users can see the statistics, however, if the view has been installed
   in their database.
  </p><p>
   Plannable queries (that is, <code class="command">SELECT</code>, <code class="command">INSERT</code>,
   <code class="command">UPDATE</code>, and <code class="command">DELETE</code>) are combined into a single
   <code class="structname">pg_stat_statements</code> entry whenever they have identical query
   structures according to an internal hash calculation.  Typically, two
   queries will be considered the same for this purpose if they are
   semantically equivalent except for the values of literal constants
   appearing in the query.  Utility commands (that is, all other commands)
   are compared strictly on the basis of their textual query strings, however.
  </p><p>
   When a constant's value has been ignored for purposes of matching the query
   to other queries, the constant is replaced by a parameter symbol, such
   as <code class="literal">$1</code>, in the <code class="structname">pg_stat_statements</code>
   display.
   The rest of the query text is that of the first query that had the
   particular <code class="structfield">queryid</code> hash value associated with the
   <code class="structname">pg_stat_statements</code> entry.
  </p><p>
   In some cases, queries with visibly different texts might get merged into a
   single <code class="structname">pg_stat_statements</code> entry.  Normally this will happen
   only for semantically equivalent queries, but there is a small chance of
   hash collisions causing unrelated queries to be merged into one entry.
   (This cannot happen for queries belonging to different users or databases,
   however.)
  </p><p>
   Since the <code class="structfield">queryid</code> hash value is computed on the
   post-parse-analysis representation of the queries, the opposite is
   also possible: queries with identical texts might appear as
   separate entries, if they have different meanings as a result of
   factors such as different <code class="varname">search_path</code> settings.
  </p><p>
   Consumers of <code class="structname">pg_stat_statements</code> may wish to use
   <code class="structfield">queryid</code> (perhaps in combination with
   <code class="structfield">dbid</code> and <code class="structfield">userid</code>) as a more stable
   and reliable identifier for each entry than its query text.
   However, it is important to understand that there are only limited
   guarantees around the stability of the <code class="structfield">queryid</code> hash
   value.  Since the identifier is derived from the
   post-parse-analysis tree, its value is a function of, among other
   things, the internal object identifiers appearing in this representation.
   This has some counterintuitive implications.  For example,
   <code class="filename">pg_stat_statements</code> will consider two apparently-identical
   queries to be distinct, if they reference a table that was dropped
   and recreated between the executions of the two queries.
   The hashing process is also sensitive to differences in
   machine architecture and other facets of the platform.
   Furthermore, it is not safe to assume that <code class="structfield">queryid</code>
   will be stable across major versions of <span class="productname">PostgreSQL</span>.
  </p><p>
   As a rule of thumb, <code class="structfield">queryid</code> values can be assumed to be
   stable and comparable only so long as the underlying server version and
   catalog metadata details stay exactly the same.  Two servers
   participating in replication based on physical WAL replay can be expected
   to have identical <code class="structfield">queryid</code> values for the same query.
   However, logical replication schemes do not promise to keep replicas
   identical in all relevant details, so <code class="structfield">queryid</code> will
   not be a useful identifier for accumulating costs across a set of logical
   replicas.  If in doubt, direct testing is recommended.
  </p><p>
   The parameter symbols used to replace constants in
   representative query texts start from the next number after the
   highest <code class="literal">$</code><em class="replaceable"><code>n</code></em> parameter in the original query
   text, or <code class="literal">$1</code> if there was none.  It's worth noting that in
   some cases there may be hidden parameter symbols that affect this
   numbering.  For example, <span class="application">PL/pgSQL</span> uses hidden parameter
   symbols to insert values of function local variables into queries, so that
   a <span class="application">PL/pgSQL</span> statement like <code class="literal">SELECT i + 1 INTO j</code>
   would have representative text like <code class="literal">SELECT i + $2</code>.
  </p><p>
   The representative query texts are kept in an external disk file, and do
   not consume shared memory.  Therefore, even very lengthy query texts can
   be stored successfully.  However, if many long query texts are
   accumulated, the external file might grow unmanageably large.  As a
   recovery method if that happens, <code class="filename">pg_stat_statements</code> may
   choose to discard the query texts, whereupon all existing entries in
   the <code class="structname">pg_stat_statements</code> view will show
   null <code class="structfield">query</code> fields, though the statistics associated with
   each <code class="structfield">queryid</code> are preserved.  If this happens, consider
   reducing <code class="varname">pg_stat_statements.max</code> to prevent
   recurrences.
  </p></div><div class="sect2" id="id-1.11.7.38.7"><div class="titlepage"><div><div><h3 class="title">F.29.2. Functions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
     <code class="function">pg_stat_statements_reset(userid Oid, dbid Oid, queryid bigint) returns void</code>
     <a id="id-1.11.7.38.7.2.1.1.2" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="function">pg_stat_statements_reset</code> discards statistics
      gathered so far by <code class="filename">pg_stat_statements</code> corresponding
      to the specified <code class="structfield">userid</code>, <code class="structfield">dbid</code>
      and <code class="structfield">queryid</code>.  If any of the parameters are not
      specified, the default value <code class="literal">0</code>(invalid) is used for
      each of them and the statistics that match with other parameters will be
      reset.  If no parameter is specified or all the specified parameters are
      <code class="literal">0</code>(invalid), it will discard all statistics.  By
      default, this function can only be executed by superusers.  Access may be
      granted to others using <code class="command">GRANT</code>.
     </p></dd><dt><span class="term">
     <code class="function">pg_stat_statements(showtext boolean) returns setof record</code>
     <a id="id-1.11.7.38.7.2.2.1.2" class="indexterm"></a>
    </span></dt><dd><p>
      The <code class="structname">pg_stat_statements</code> view is defined in
      terms of a function also named <code class="function">pg_stat_statements</code>.
      It is possible for clients to call
      the <code class="function">pg_stat_statements</code> function directly, and by
      specifying <code class="literal">showtext := false</code> have query text be
      omitted (that is, the <code class="literal">OUT</code> argument that corresponds
      to the view's <code class="structfield">query</code> column will return nulls).  This
      feature is intended to support external tools that might wish to avoid
      the overhead of repeatedly retrieving query texts of indeterminate
      length.  Such tools can instead cache the first query text observed
      for each entry themselves, since that is
      all <code class="filename">pg_stat_statements</code> itself does, and then retrieve
      query texts only as needed.  Since the server stores query texts in a
      file, this approach may reduce physical I/O for repeated examination
      of the <code class="structname">pg_stat_statements</code> data.
     </p></dd></dl></div></div><div class="sect2" id="id-1.11.7.38.8"><div class="titlepage"><div><div><h3 class="title">F.29.3. Configuration Parameters</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
     <code class="varname">pg_stat_statements.max</code> (<code class="type">integer</code>)
    </span></dt><dd><p>
      <code class="varname">pg_stat_statements.max</code> is the maximum number of
      statements tracked by the module (i.e., the maximum number of rows
      in the <code class="structname">pg_stat_statements</code> view).  If more distinct
      statements than that are observed, information about the least-executed
      statements is discarded.
      The default value is 5000.
      This parameter can only be set at server start.
     </p></dd><dt><span class="term">
     <code class="varname">pg_stat_statements.track</code> (<code class="type">enum</code>)
    </span></dt><dd><p>
      <code class="varname">pg_stat_statements.track</code> controls which statements
      are counted by the module.
      Specify <code class="literal">top</code> to track top-level statements (those issued
      directly by clients), <code class="literal">all</code> to also track nested statements
      (such as statements invoked within functions), or <code class="literal">none</code> to
      disable statement statistics collection.
      The default value is <code class="literal">top</code>.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">pg_stat_statements.track_utility</code> (<code class="type">boolean</code>)
    </span></dt><dd><p>
      <code class="varname">pg_stat_statements.track_utility</code> controls whether
      utility commands are tracked by the module.  Utility commands are
      all those other than <code class="command">SELECT</code>, <code class="command">INSERT</code>,
      <code class="command">UPDATE</code> and <code class="command">DELETE</code>.
      The default value is <code class="literal">on</code>.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">pg_stat_statements.save</code> (<code class="type">boolean</code>)
    </span></dt><dd><p>
      <code class="varname">pg_stat_statements.save</code> specifies whether to
      save statement statistics across server shutdowns.
      If it is <code class="literal">off</code> then statistics are not saved at
      shutdown nor reloaded at server start.
      The default value is <code class="literal">on</code>.
      This parameter can only be set in the <code class="filename">postgresql.conf</code>
      file or on the server command line.
     </p></dd></dl></div><p>
   The module requires additional shared memory proportional to
   <code class="varname">pg_stat_statements.max</code>.  Note that this
   memory is consumed whenever the module is loaded, even if
   <code class="varname">pg_stat_statements.track</code> is set to <code class="literal">none</code>.
  </p><p>
   These parameters must be set in <code class="filename">postgresql.conf</code>.
   Typical usage might be:

</p><pre class="programlisting">
# postgresql.conf
shared_preload_libraries = 'pg_stat_statements'

pg_stat_statements.max = 10000
pg_stat_statements.track = all
</pre><p>
  </p></div><div class="sect2" id="id-1.11.7.38.9"><div class="titlepage"><div><div><h3 class="title">F.29.4. Sample Output</h3></div></div></div><pre class="screen">
bench=# SELECT pg_stat_statements_reset();

$ pgbench -i bench
$ pgbench -c10 -t300 bench

bench=# \x
bench=# SELECT query, calls, total_time, rows, 100.0 * shared_blks_hit /
               nullif(shared_blks_hit + shared_blks_read, 0) AS hit_percent
          FROM pg_stat_statements ORDER BY total_time DESC LIMIT 5;
-[ RECORD 1 ]--------------------------------------------------------------------
query       | UPDATE pgbench_branches SET bbalance = bbalance + $1 WHERE bid = $2
calls       | 3000
total_time  | 25565.855387
rows        | 3000
hit_percent | 100.0000000000000000
-[ RECORD 2 ]--------------------------------------------------------------------
query       | UPDATE pgbench_tellers SET tbalance = tbalance + $1 WHERE tid = $2
calls       | 3000
total_time  | 20756.669379
rows        | 3000
hit_percent | 100.0000000000000000
-[ RECORD 3 ]--------------------------------------------------------------------
query       | copy pgbench_accounts from stdin
calls       | 1
total_time  | 291.865911
rows        | 100000
hit_percent | 100.0000000000000000
-[ RECORD 4 ]--------------------------------------------------------------------
query       | UPDATE pgbench_accounts SET abalance = abalance + $1 WHERE aid = $2
calls       | 3000
total_time  | 271.232977
rows        | 3000
hit_percent | 98.5723926698852723
-[ RECORD 5 ]--------------------------------------------------------------------
query       | alter table pgbench_accounts add primary key (aid)
calls       | 1
total_time  | 160.588563
rows        | 0
hit_percent | 100.0000000000000000


bench=# SELECT pg_stat_statements_reset(0,0,s.queryid) FROM pg_stat_statements AS s
            WHERE s.query = 'UPDATE pgbench_branches SET bbalance = bbalance + $1 WHERE bid = $2';

bench=# SELECT query, calls, total_time, rows, 100.0 * shared_blks_hit /
               nullif(shared_blks_hit + shared_blks_read, 0) AS hit_percent
          FROM pg_stat_statements ORDER BY total_time DESC LIMIT 5;
-[ RECORD 1 ]--------------------------------------------------------------------
query       | UPDATE pgbench_tellers SET tbalance = tbalance + $1 WHERE tid = $2
calls       | 3000
total_time  | 20756.669379
rows        | 3000
hit_percent | 100.0000000000000000
-[ RECORD 2 ]--------------------------------------------------------------------
query       | copy pgbench_accounts from stdin
calls       | 1
total_time  | 291.865911
rows        | 100000
hit_percent | 100.0000000000000000
-[ RECORD 3 ]--------------------------------------------------------------------
query       | UPDATE pgbench_accounts SET abalance = abalance + $1 WHERE aid = $2
calls       | 3000
total_time  | 271.232977
rows        | 3000
hit_percent | 98.5723926698852723
-[ RECORD 4 ]--------------------------------------------------------------------
query       | alter table pgbench_accounts add primary key (aid)
calls       | 1
total_time  | 160.588563
rows        | 0
hit_percent | 100.0000000000000000
-[ RECORD 5 ]--------------------------------------------------------------------
query       | vacuum analyze pgbench_accounts
calls       | 1
total_time  | 136.448116
rows        | 0
hit_percent | 99.9201915403032721

bench=# SELECT pg_stat_statements_reset(0,0,0);

bench=# SELECT query, calls, total_time, rows, 100.0 * shared_blks_hit /
               nullif(shared_blks_hit + shared_blks_read, 0) AS hit_percent
          FROM pg_stat_statements ORDER BY total_time DESC LIMIT 5;
-[ RECORD 1 ]---------------------------------------
query       | SELECT pg_stat_statements_reset(0,0,0)
calls       | 1
total_time  | 0.189497
rows        | 1
hit_percent | 

</pre></div><div class="sect2" id="id-1.11.7.38.10"><div class="titlepage"><div><div><h3 class="title">F.29.5. Authors</h3></div></div></div><p>
   Takahiro Itagaki <code class="email">&lt;<a class="email" href="mailto:itagaki.takahiro@oss.ntt.co.jp">itagaki.takahiro@oss.ntt.co.jp</a>&gt;</code>.
   Query normalization added by Peter Geoghegan <code class="email">&lt;<a class="email" href="mailto:peter@2ndquadrant.com">peter@2ndquadrant.com</a>&gt;</code>.
  </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pgrowlocks.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="pgstattuple.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.28. pgrowlocks </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> F.30. pgstattuple</td></tr></table></div></body></html>