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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!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.30. pg_prewarm — preload relation data into buffer caches</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="pgfreespacemap.html" title="F.29. pg_freespacemap — examine the free space map" /><link rel="next" href="pgrowlocks.html" title="F.31. pgrowlocks — show a table's row locking information" /></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.30. pg_prewarm — preload relation data into buffer caches</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pgfreespacemap.html" title="F.29. pg_freespacemap — examine the free space map">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 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgrowlocks.html" title="F.31. pgrowlocks — show a table's row locking information">Next</a></td></tr></table><hr /></div><div class="sect1" id="PGPREWARM"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.30. pg_prewarm — preload relation data into buffer caches <a href="#PGPREWARM" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgprewarm.html#PGPREWARM-FUNCS">F.30.1. Functions</a></span></dt><dt><span class="sect2"><a href="pgprewarm.html#PGPREWARM-CONFIG-PARAMS">F.30.2. Configuration Parameters</a></span></dt><dt><span class="sect2"><a href="pgprewarm.html#PGPREWARM-AUTHOR">F.30.3. Author</a></span></dt></dl></div><a id="id-1.11.7.40.2" class="indexterm"></a><p>3  The <code class="filename">pg_prewarm</code> module provides a convenient way4  to load relation data into either the operating system buffer cache5  or the <span class="productname">PostgreSQL</span> buffer cache.  Prewarming6  can be performed manually using the <code class="filename">pg_prewarm</code> function,7  or can be performed automatically by including <code class="literal">pg_prewarm</code> in8  <a class="xref" href="runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES">shared_preload_libraries</a>.  In the latter case, the9  system will run a background worker which periodically records the contents10  of shared buffers in a file called <code class="filename">autoprewarm.blocks</code> and11  will, using 2 background workers, reload those same blocks after a restart.12 </p><div class="sect2" id="PGPREWARM-FUNCS"><div class="titlepage"><div><div><h3 class="title">F.30.1. Functions <a href="#PGPREWARM-FUNCS" class="id_link">#</a></h3></div></div></div><pre class="synopsis">13pg_prewarm(regclass, mode text default 'buffer', fork text default 'main',14           first_block int8 default null,15           last_block int8 default null) RETURNS int816</pre><p>17   The first argument is the relation to be prewarmed.  The second argument18   is the prewarming method to be used, as further discussed below; the third19   is the relation fork to be prewarmed, usually <code class="literal">main</code>.20   The fourth argument is the first block number to prewarm21   (<code class="literal">NULL</code> is accepted as a synonym for zero).  The fifth22   argument is the last block number to prewarm (<code class="literal">NULL</code>23   means prewarm through the last block in the relation).  The return value24   is the number of blocks prewarmed.25  </p><p>26   There are three available prewarming methods.  <code class="literal">prefetch</code>27   issues asynchronous prefetch requests to the operating system, if this is28   supported, or throws an error otherwise.  <code class="literal">read</code> reads29   the requested range of blocks; unlike <code class="literal">prefetch</code>, this is30   synchronous and supported on all platforms and builds, but may be slower.31   <code class="literal">buffer</code> reads the requested range of blocks into the32   database buffer cache.33  </p><p>34   Note that with any of these methods, attempting to prewarm more blocks than35   can be cached — by the OS when using <code class="literal">prefetch</code> or36   <code class="literal">read</code>, or by <span class="productname">PostgreSQL</span> when37   using <code class="literal">buffer</code> — will likely result in lower-numbered38   blocks being evicted as higher numbered blocks are read in.  Prewarmed data39   also enjoys no special protection from cache evictions, so it is possible40   that other system activity may evict the newly prewarmed blocks shortly41   after they are read; conversely, prewarming may also evict other data from42   cache. For these reasons, prewarming is typically most useful at startup,43   when caches are largely empty.44  </p><pre class="synopsis">45autoprewarm_start_worker() RETURNS void46</pre><p>47   Launch the main autoprewarm worker.  This will normally happen48   automatically, but is useful if automatic prewarm was not configured at49   server startup time and you wish to start up the worker at a later time.50  </p><pre class="synopsis">51autoprewarm_dump_now() RETURNS int852</pre><p>53   Update <code class="filename">autoprewarm.blocks</code> immediately.  This may be useful54   if the autoprewarm worker is not running but you anticipate running it55   after the next restart.  The return value is the number of records written56   to <code class="filename">autoprewarm.blocks</code>.57  </p></div><div class="sect2" id="PGPREWARM-CONFIG-PARAMS"><div class="titlepage"><div><div><h3 class="title">F.30.2. Configuration Parameters <a href="#PGPREWARM-CONFIG-PARAMS" class="id_link">#</a></h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">58     <code class="varname">pg_prewarm.autoprewarm</code> (<code class="type">boolean</code>)59     <a id="id-1.11.7.40.5.2.1.1.3" class="indexterm"></a>60    </span></dt><dd><p>61      Controls whether the server should run the autoprewarm worker. This is62      on by default. This parameter can only be set at server start.63     </p></dd></dl></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">64     <code class="varname">pg_prewarm.autoprewarm_interval</code> (<code class="type">integer</code>)65     <a id="id-1.11.7.40.5.3.1.1.3" class="indexterm"></a>66    </span></dt><dd><p>67      This is the interval between updates to <code class="literal">autoprewarm.blocks</code>.68      The default is 300 seconds. If set to 0, the file will not be69      dumped at regular intervals, but only when the server is shut down.70     </p></dd></dl></div><p>71   These parameters must be set in <code class="filename">postgresql.conf</code>.72   Typical usage might be:73  </p><pre class="programlisting">74# postgresql.conf75shared_preload_libraries = 'pg_prewarm'76 77pg_prewarm.autoprewarm = true78pg_prewarm.autoprewarm_interval = 300s79 80</pre></div><div class="sect2" id="PGPREWARM-AUTHOR"><div class="titlepage"><div><div><h3 class="title">F.30.3. Author <a href="#PGPREWARM-AUTHOR" class="id_link">#</a></h3></div></div></div><p>81   Robert Haas <code class="email">&lt;<a class="email" href="mailto:rhaas@postgresql.org">rhaas@postgresql.org</a>&gt;</code>82  </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pgfreespacemap.html" title="F.29. pg_freespacemap — examine the free space map">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="pgrowlocks.html" title="F.31. pgrowlocks — show a table's row locking information">Next</a></td></tr><tr><td width="40%" align="left" valign="top">F.29. pg_freespacemap — examine the free space map </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"> F.31. pgrowlocks — show a table's row locking information</td></tr></table></div></body></html>