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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_overexplain — allow EXPLAIN to dump even more details</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="pglogicalinspect.html" title="F.28. pg_logicalinspect — logical decoding components inspection" /><link rel="next" href="pgprewarm.html" title="F.30. pg_prewarm — preload relation data into buffer caches" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.29. pg_overexplain — allow EXPLAIN to dump even more details</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pglogicalinspect.html" title="F.28. pg_logicalinspect — logical decoding components inspection">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</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="pgprewarm.html" title="F.30. pg_prewarm — preload relation data into buffer caches">Next</a></td></tr></table><hr /></div><div class="sect1" id="PGOVEREXPLAIN"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.29. pg_overexplain — allow EXPLAIN to dump even more details <a href="#PGOVEREXPLAIN" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgoverexplain.html#PGOVEREXPLAIN-DEBUG">F.29.1. EXPLAIN (DEBUG)</a></span></dt><dt><span class="sect2"><a href="pgoverexplain.html#PGOVEREXPLAIN-RANGE-TABLE">F.29.2. EXPLAIN (RANGE_TABLE)</a></span></dt><dt><span class="sect2"><a href="pgoverexplain.html#PGOVEREXPLAIN-AUTHOR">F.29.3. Author</a></span></dt></dl></div><a id="id-1.11.7.39.2" class="indexterm"></a><p>
  The <code class="filename">pg_overexplain</code> module extends <code class="command">EXPLAIN</code>
  with new options that provide additional output. It is mostly intended to
  assist with debugging of and development of the planner, rather than for
  general use. Since this module displays internal details of planner data
  structures, it may be necessary to refer to the source code to make sense
  of the output. Furthermore, the output is likely to change whenever (and as
  often as) those data structures change.
 </p><p>
  To use it, simply load it into the server.  You can load it into an
  individual session:

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

  You can also preload it into some or all sessions by including
  <code class="literal">pg_overexplain</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>.
 </p><div class="sect2" id="PGOVEREXPLAIN-DEBUG"><div class="titlepage"><div><div><h3 class="title">F.29.1. EXPLAIN (DEBUG) <a href="#PGOVEREXPLAIN-DEBUG" class="id_link">#</a></h3></div></div></div><p>
   The <code class="literal">DEBUG</code> option displays miscellaneous information from
   the plan tree that is not normally shown because it is not expected to be
   of general interest. For each individual plan node, it will display the
   following fields.  See <code class="structname">Plan</code> in
   <code class="filename">nodes/plannodes.h</code> for additional documentation of these
   fields.
  </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
     <code class="literal">Disabled Nodes</code>. Normal <code class="command">EXPLAIN</code>
     determines whether a node is disabled by checking whether the node's
     count of disabled nodes is larger than the sum of the counts for the
     underlying nodes. This option shows the raw counter value.
    </p></li><li class="listitem"><p>
     <code class="literal">Parallel Safe</code>. Indicates whether it would be safe for
     a plan tree node to appear beneath a <code class="literal">Gather</code> or
     <code class="literal">Gather Merge</code> node, regardless of whether it is
     actually below such a node.
    </p></li><li class="listitem"><p>
     <code class="literal">Plan Node ID</code>. An internal ID number that should be
     unique for every node in the plan tree. It is used to coordinate parallel
     query activity.
    </p></li><li class="listitem"><p>
     <code class="literal">extParam</code> and <code class="literal">allParam</code>. Information
     about which numbered parameters affect this plan node or its children. In
     text mode, these fields are only displayed if they are non-empty sets.
    </p></li></ul></div><p>
   Once per query, the <code class="literal">DEBUG</code> option will display the
   following fields. See <code class="structname">PlannedStmt</code> in
   <code class="filename">nodes/plannodes.h</code> for additional detail.
  </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
     <code class="literal">Command Type</code>. For example, <code class="literal">select</code>
     or <code class="literal">update</code>.
    </p></li><li class="listitem"><p>
     <code class="literal">Flags</code>. A comma-separated list of Boolean structure
     member names from the <code class="structname">PlannedStmt</code> that are set to
     <code class="literal">true</code>. It covers the following structure members:
     <code class="literal">hasReturning</code>, <code class="literal">hasModifyingCTE</code>,
     <code class="literal">canSetTag</code>, <code class="literal">transientPlan</code>,
     <code class="literal">dependsOnRole</code>, <code class="literal">parallelModeNeeded</code>.
    </p></li><li class="listitem"><p>
     <code class="literal">Subplans Needing Rewind</code>. Integer IDs of subplans that
     may need to be rewound by the executor.
    </p></li><li class="listitem"><p>
     <code class="literal">Relation OIDs</code>. OIDs of relations upon which this plan
     depends.
    </p></li><li class="listitem"><p>
     <code class="literal">Executor Parameter Types</code>. Type OID for each executor parameter
     (e.g. when a nested loop is chosen and a parameter is used to pass a value down
     to an inner index scan). Does not include parameters supplied to a prepared
     statement by the user.
    </p></li><li class="listitem"><p>
     <code class="literal">Parse Location</code>. Location within the query string
     supplied to the planner where this query's text can be found. May be
     <code class="literal">Unknown</code> in some contexts. Otherwise, may be
     <code class="literal">NNN to end</code> for some integer <code class="literal">NNN</code> or
     <code class="literal">NNN for MMM bytes</code> for some integers
     <code class="literal">NNN</code> and <code class="literal">MMM</code>.
    </p></li></ul></div></div><div class="sect2" id="PGOVEREXPLAIN-RANGE-TABLE"><div class="titlepage"><div><div><h3 class="title">F.29.2. EXPLAIN (RANGE_TABLE) <a href="#PGOVEREXPLAIN-RANGE-TABLE" class="id_link">#</a></h3></div></div></div><p>
   The <code class="literal">RANGE_TABLE</code> option displays information from the
   plan tree specifically concerning the query's range table. Range table
   entries correspond roughly to items appearing in the query's
   <code class="literal">FROM</code> clause, but with numerous exceptions. For example,
   subqueries that are proved unnecessary may be deleted from the range table
   entirely, while inheritance expansion adds range table entries for child
   tables that are not named directly in the query.
  </p><p>
   Range table entries are generally referenced within the query plan by a
   range table index, or RTI. Plan nodes that reference one or more RTIs will
   be labelled accordingly, using one of the following fields: <code class="literal">Scan
   RTI</code>, <code class="literal">Nominal RTI</code>, <code class="literal">Exclude Relation
   RTI</code>, <code class="literal">Append RTIs</code>.
  </p><p>
   In addition, the query as a whole may maintain lists of range table indexes
   that are needed for various purposes. These lists will be displayed once
   per query, labelled as appropriate as <code class="literal">Unprunable RTIs</code> or
   <code class="literal">Result RTIs</code>. In text mode, these fields are only
   displayed if they are non-empty sets.
  </p><p>
   Finally, but most importantly, the <code class="literal">RANGE_TABLE</code> option
   will display a dump of the query's entire range table. Each range table
   entry is labelled with the appropriate range table index, the kind of range
   table entry (e.g.  <code class="literal">relation</code>,
   <code class="literal">subquery</code>, or <code class="literal">join</code>), followed by the
   contents of various range table entry fields that are not normally part of
   <code class="command">EXPLAIN</code> output. Some of these fields are only displayed
   for certain kinds of range table entries. For example,
   <code class="literal">Eref</code> is displayed for all types of range table entries,
   but <code class="literal">CTE Name</code> is displayed only for range table entries
   of type <code class="literal">cte</code>.
  </p><p>
   For more information about range table entries, see the definition of
   <code class="structname">RangeTblEntry</code> in <code class="filename">nodes/parsenodes.h</code>.
  </p></div><div class="sect2" id="PGOVEREXPLAIN-AUTHOR"><div class="titlepage"><div><div><h3 class="title">F.29.3. Author <a href="#PGOVEREXPLAIN-AUTHOR" class="id_link">#</a></h3></div></div></div><p>
   Robert Haas <code class="email">&lt;<a class="email" href="mailto:rhaas@postgresql.org">rhaas@postgresql.org</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="pglogicalinspect.html" title="F.28. pg_logicalinspect — logical decoding components inspection">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="pgprewarm.html" title="F.30. pg_prewarm — preload relation data into buffer caches">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.28. pg_logicalinspect — logical decoding components inspection </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"> F.30. pg_prewarm — preload relation data into buffer caches</td></tr></table></div></body></html>