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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>pg_test_fsync</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="app-pgrewind.html" title="pg_rewind" /><link rel="next" href="pgtesttiming.html" title="pg_test_timing" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center"><span class="application">pg_test_fsync</span></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="app-pgrewind.html" title="pg_rewind">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="reference-server.html" title="PostgreSQL Server Applications">Up</a></td><th width="60%" align="center">PostgreSQL Server Applications</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgtesttiming.html" title="pg_test_timing">Next</a></td></tr></table><hr /></div><div class="refentry" id="PGTESTFSYNC"><div class="titlepage"></div><a id="id-1.9.5.10.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle"><span class="application">pg_test_fsync</span></span></h2><p>pg_test_fsync — determine fastest <code class="varname">wal_sync_method</code> for <span class="productname">PostgreSQL</span></p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="cmdsynopsis"><p id="id-1.9.5.10.4.1"><code class="command">pg_test_fsync</code> [<em class="replaceable"><code>option</code></em>...]</p></div></div><div class="refsect1" id="id-1.9.5.10.5"><h2>Description</h2><p>
<span class="application">pg_test_fsync</span> is intended to give you a reasonable
idea of what the fastest <a class="xref" href="runtime-config-wal.html#GUC-WAL-SYNC-METHOD">wal_sync_method</a> is on your
specific system,
as well as supplying diagnostic information in the event of an identified I/O
problem. However, differences shown by
<span class="application">pg_test_fsync</span> might not make any significant
difference in real database throughput, especially since many database servers
are not speed-limited by their write-ahead logs.
<span class="application">pg_test_fsync</span> reports average file sync operation
time in microseconds for each <code class="literal">wal_sync_method</code>, which can also be used to
inform efforts to optimize the value of <a class="xref" href="runtime-config-wal.html#GUC-COMMIT-DELAY">commit_delay</a>.
</p></div><div class="refsect1" id="id-1.9.5.10.6"><h2>Options</h2><p>
<span class="application">pg_test_fsync</span> accepts the following
command-line options:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-f</code><br /></span><span class="term"><code class="option">--filename</code></span></dt><dd><p>
Specifies the file name to write test data in.
This file should be in the same file system that the
<code class="filename">pg_wal</code> directory is or will be placed in.
(<code class="filename">pg_wal</code> contains the <acronym class="acronym">WAL</acronym> files.)
The default is <code class="filename">pg_test_fsync.out</code> in the current
directory.
</p></dd><dt><span class="term"><code class="option">-s</code><br /></span><span class="term"><code class="option">--secs-per-test</code></span></dt><dd><p>
Specifies the number of seconds for each test. The more time
per test, the greater the test's accuracy, but the longer it takes
to run. The default is 5 seconds, which allows the program to
complete in under 2 minutes.
</p></dd><dt><span class="term"><code class="option">-V</code><br /></span><span class="term"><code class="option">--version</code></span></dt><dd><p>
Print the <span class="application">pg_test_fsync</span> version and exit.
</p></dd><dt><span class="term"><code class="option">-?</code><br /></span><span class="term"><code class="option">--help</code></span></dt><dd><p>
Show help about <span class="application">pg_test_fsync</span> command line
arguments, and exit.
</p></dd></dl></div><p>
</p></div><div class="refsect1" id="id-1.9.5.10.7"><h2>Environment</h2><p>
The environment variable <code class="envar">PG_COLOR</code> specifies whether to use
color in diagnostic messages. Possible values are
<code class="literal">always</code>, <code class="literal">auto</code> and
<code class="literal">never</code>.
</p></div><div class="refsect1" id="id-1.9.5.10.8"><h2>See Also</h2><span class="simplelist"><a class="xref" href="app-postgres.html" title="postgres"><span class="refentrytitle"><span class="application">postgres</span></span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="app-pgrewind.html" title="pg_rewind">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="reference-server.html" title="PostgreSQL Server Applications">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="pgtesttiming.html" title="pg_test_timing">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span class="application">pg_rewind</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> <span class="application">pg_test_timing</span></td></tr></table></div></body></html>
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