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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.4. auto_explain</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="auth-delay.html" title="F.3. auth_delay" /><link rel="next" href="bloom.html" title="F.5. bloom" /></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.4. auto_explain</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="auth-delay.html" title="F.3. auth_delay">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="bloom.html" title="F.5. bloom">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="AUTO-EXPLAIN"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.4. auto_explain</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="auto-explain.html#id-1.11.7.13.5">F.4.1. Configuration Parameters</a></span></dt><dt><span class="sect2"><a href="auto-explain.html#id-1.11.7.13.6">F.4.2. Example</a></span></dt><dt><span class="sect2"><a href="auto-explain.html#id-1.11.7.13.7">F.4.3. Author</a></span></dt></dl></div><a id="id-1.11.7.13.2" class="indexterm"></a><p>
  The <code class="filename">auto_explain</code> module provides a means for
  logging execution plans of slow statements automatically, without
  having to run <a class="xref" href="sql-explain.html" title="EXPLAIN"><span class="refentrytitle">EXPLAIN</span></a>
  by hand.  This is especially helpful for tracking down un-optimized queries
  in large applications.
 </p><p>
  The module provides no SQL-accessible functions.  To use it, simply
  load it into the server.  You can load it into an individual session:

</p><pre class="programlisting">
LOAD 'auto_explain';
</pre><p>

  (You must be superuser to do that.)  More typical usage is to preload
  it into some or all sessions by including <code class="literal">auto_explain</code> in
  <a class="xref" href="runtime-config-client.html#GUC-SESSION-PRELOAD-LIBRARIES">session_preload_libraries</a> or
  <a class="xref" href="runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES">shared_preload_libraries</a> in
  <code class="filename">postgresql.conf</code>.  Then you can track unexpectedly slow queries
  no matter when they happen.  Of course there is a price in overhead for
  that.
 </p><div class="sect2" id="id-1.11.7.13.5"><div class="titlepage"><div><div><h3 class="title">F.4.1. Configuration Parameters</h3></div></div></div><p>
  There are several configuration parameters that control the behavior of
  <code class="filename">auto_explain</code>.  Note that the default behavior is
  to do nothing, so you must set at least
  <code class="varname">auto_explain.log_min_duration</code> if you want any results.
 </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">
     <code class="varname">auto_explain.log_min_duration</code> (<code class="type">integer</code>)
     <a id="id-1.11.7.13.5.3.1.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_min_duration</code> is the minimum statement
      execution time, in milliseconds, that will cause the statement's plan to
      be logged. Setting this to <code class="literal">0</code> logs all plans.
      <code class="literal">-1</code> (the default) disables logging of plans. For
      example, if you set it to <code class="literal">250ms</code> then all statements
      that run 250ms or longer will be logged. Only superusers can change this
      setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.log_analyze</code> (<code class="type">boolean</code>)
     <a id="id-1.11.7.13.5.3.2.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_analyze</code> causes <code class="command">EXPLAIN ANALYZE</code>
      output, rather than just <code class="command">EXPLAIN</code> output, to be printed
      when an execution plan is logged. This parameter is off by default.
      Only superusers can change this setting.
     </p><div class="note"><h3 class="title">Note</h3><p>
       When this parameter is on, per-plan-node timing occurs for all
       statements executed, whether or not they run long enough to actually
       get logged.  This can have an extremely negative impact on performance.
       Turning off <code class="varname">auto_explain.log_timing</code> ameliorates the
       performance cost, at the price of obtaining less information.
      </p></div></dd><dt><span class="term">
     <code class="varname">auto_explain.log_buffers</code> (<code class="type">boolean</code>)
     <a id="id-1.11.7.13.5.3.3.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_buffers</code> controls whether buffer
      usage statistics are printed when an execution plan is logged; it's
      equivalent to the <code class="literal">BUFFERS</code> option of <code class="command">EXPLAIN</code>.
      This parameter has no effect
      unless <code class="varname">auto_explain.log_analyze</code> is enabled.
      This parameter is off by default.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.log_timing</code> (<code class="type">boolean</code>)
     <a id="id-1.11.7.13.5.3.4.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_timing</code> controls whether per-node
      timing information is printed when an execution plan is logged; it's
      equivalent to the <code class="literal">TIMING</code> option of <code class="command">EXPLAIN</code>.
      The overhead of repeatedly reading the system clock can slow down
      queries significantly on some systems, so it may be useful to set this
      parameter to off when only actual row counts, and not exact times, are
      needed.
      This parameter has no effect
      unless <code class="varname">auto_explain.log_analyze</code> is enabled.
      This parameter is on by default.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.log_triggers</code> (<code class="type">boolean</code>)
     <a id="id-1.11.7.13.5.3.5.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_triggers</code> causes trigger
      execution statistics to be included when an execution plan is logged.
      This parameter has no effect
      unless <code class="varname">auto_explain.log_analyze</code> is enabled.
      This parameter is off by default.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.log_verbose</code> (<code class="type">boolean</code>)
     <a id="id-1.11.7.13.5.3.6.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_verbose</code> controls whether verbose
      details are printed when an execution plan is logged; it's
      equivalent to the <code class="literal">VERBOSE</code> option of <code class="command">EXPLAIN</code>.
      This parameter is off by default.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.log_settings</code> (<code class="type">boolean</code>)
     <a id="id-1.11.7.13.5.3.7.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_settings</code> controls whether information
      about modified configuration options are printed when execution plan is logged.
      Only options affecting query planning with value different from the built-in
      default value are included in the output.  This parameter is off by default.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.log_format</code> (<code class="type">enum</code>)
     <a id="id-1.11.7.13.5.3.8.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_format</code> selects the
      <code class="command">EXPLAIN</code> output format to be used.
      The allowed values are <code class="literal">text</code>, <code class="literal">xml</code>,
      <code class="literal">json</code>, and <code class="literal">yaml</code>.  The default is text.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.log_level</code> (<code class="type">enum</code>)
     <a id="id-1.11.7.13.5.3.9.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_level</code> selects the log level at which
      auto_explain will log the query plan.
      Valid values are <code class="literal">DEBUG5</code>, <code class="literal">DEBUG4</code>,
      <code class="literal">DEBUG3</code>, <code class="literal">DEBUG2</code>,
      <code class="literal">DEBUG1</code>, <code class="literal">INFO</code>,
      <code class="literal">NOTICE</code>, <code class="literal">WARNING</code>,
      and <code class="literal">LOG</code>. The default is <code class="literal">LOG</code>.
      Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.log_nested_statements</code> (<code class="type">boolean</code>)
     <a id="id-1.11.7.13.5.3.10.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.log_nested_statements</code> causes nested
      statements (statements executed inside a function) to be considered
      for logging.  When it is off, only top-level query plans are logged. This
      parameter is off by default. Only superusers can change this setting.
     </p></dd><dt><span class="term">
     <code class="varname">auto_explain.sample_rate</code> (<code class="type">real</code>)
     <a id="id-1.11.7.13.5.3.11.1.3" class="indexterm"></a>
    </span></dt><dd><p>
      <code class="varname">auto_explain.sample_rate</code> causes auto_explain to only
      explain a fraction of the statements in each session.  The default is 1,
      meaning explain all the queries.  In case of nested statements, either all
      will be explained or none. Only superusers can change this setting.
     </p></dd></dl></div><p>
   In ordinary usage, these parameters are set
   in <code class="filename">postgresql.conf</code>, although superusers can alter them
   on-the-fly within their own sessions.
   Typical usage might be:
  </p><pre class="programlisting">
# postgresql.conf
session_preload_libraries = 'auto_explain'

auto_explain.log_min_duration = '3s'
</pre></div><div class="sect2" id="id-1.11.7.13.6"><div class="titlepage"><div><div><h3 class="title">F.4.2. Example</h3></div></div></div><pre class="programlisting">
postgres=# LOAD 'auto_explain';
postgres=# SET auto_explain.log_min_duration = 0;
postgres=# SET auto_explain.log_analyze = true;
postgres=# SELECT count(*)
           FROM pg_class, pg_index
           WHERE oid = indrelid AND indisunique;
</pre><p>
   This might produce log output such as:
  </p><pre class="screen">
LOG:  duration: 3.651 ms  plan:
  Query Text: SELECT count(*)
              FROM pg_class, pg_index
              WHERE oid = indrelid AND indisunique;
  Aggregate  (cost=16.79..16.80 rows=1 width=0) (actual time=3.626..3.627 rows=1 loops=1)
    -&gt;  Hash Join  (cost=4.17..16.55 rows=92 width=0) (actual time=3.349..3.594 rows=92 loops=1)
          Hash Cond: (pg_class.oid = pg_index.indrelid)
          -&gt;  Seq Scan on pg_class  (cost=0.00..9.55 rows=255 width=4) (actual time=0.016..0.140 rows=255 loops=1)
          -&gt;  Hash  (cost=3.02..3.02 rows=92 width=4) (actual time=3.238..3.238 rows=92 loops=1)
                Buckets: 1024  Batches: 1  Memory Usage: 4kB
                -&gt;  Seq Scan on pg_index  (cost=0.00..3.02 rows=92 width=4) (actual time=0.008..3.187 rows=92 loops=1)
                      Filter: indisunique
</pre></div><div class="sect2" id="id-1.11.7.13.7"><div class="titlepage"><div><div><h3 class="title">F.4.3. Author</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>
  </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="auth-delay.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="bloom.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.3. auth_delay </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> F.5. bloom</td></tr></table></div></body></html>