doc/src/sgml/ref/pgtestfsync.sgml

   1 <!--
   2 doc/src/sgml/ref/pgtestfsync.sgml
   3 PostgreSQL documentation
   4 -->
   5
   6 <refentry id="pgtestfsync">
   7  <indexterm zone="pgtestfsync">
   8   <primary>pg_test_fsync</primary>
   9  </indexterm>
  10
  11  <refmeta>
  12   <refentrytitle><application>pg_test_fsync</application></refentrytitle>
  13   <manvolnum>1</manvolnum>
  14   <refmiscinfo>Application</refmiscinfo>
  15  </refmeta>
  16
  17  <refnamediv>
  18   <refname>pg_test_fsync</refname>
  19   <refpurpose>determine fastest <varname>wal_sync_method</varname> for <productname>PostgreSQL</productname></refpurpose>
  20  </refnamediv>
  21
  22  <refsynopsisdiv>
  23   <cmdsynopsis>
  24    <command>pg_test_fsync</command>
  25    <arg rep="repeat"><replaceable>option</replaceable></arg>
  26   </cmdsynopsis>
  27  </refsynopsisdiv>
  28
  29  <refsect1>
  30   <title>Description</title>
  31
  32  <para>
  33   <application>pg_test_fsync</application> is intended to give you a reasonable
  34   idea of what the fastest <xref linkend="guc-wal-sync-method"/> is on your
  35   specific system,
  36   as well as supplying diagnostic information in the event of an identified I/O
  37   problem.  However, differences shown by
  38   <application>pg_test_fsync</application> might not make any significant
  39   difference in real database throughput, especially since many database servers
  40   are not speed-limited by their write-ahead logs.
  41   <application>pg_test_fsync</application> reports average file sync operation
  42   time in microseconds for each <literal>wal_sync_method</literal>, which can also be used to
  43   inform efforts to optimize the value of <xref linkend="guc-commit-delay"/>.
  44  </para>
  45  </refsect1>
  46
  47  <refsect1>
  48   <title>Options</title>
  49
  50    <para>
  51     <application>pg_test_fsync</application> accepts the following
  52     command-line options:
  53
  54     <variablelist>
  55
  56      <varlistentry>
  57       <term><option>-f</option></term>
  58       <term><option>--filename</option></term>
  59       <listitem>
  60        <para>
  61         Specifies the file name to write test data in.
  62         This file should be in the same file system that the
  63         <filename>pg_wal</filename> directory is or will be placed in.
  64         (<filename>pg_wal</filename> contains the <acronym>WAL</acronym> files.)
  65         The default is <filename>pg_test_fsync.out</filename> in the current
  66         directory.
  67        </para>
  68       </listitem>
  69      </varlistentry>
  70
  71      <varlistentry>
  72       <term><option>-s</option></term>
  73       <term><option>--secs-per-test</option></term>
  74       <listitem>
  75        <para>
  76         Specifies the number of seconds for each test.  The more time
  77         per test, the greater the test's accuracy, but the longer it takes
  78         to run.  The default is 5 seconds, which allows the program to
  79         complete in under 2 minutes.
  80        </para>
  81       </listitem>
  82      </varlistentry>
  83
  84      <varlistentry>
  85       <term><option>-V</option></term>
  86       <term><option>--version</option></term>
  87       <listitem>
  88        <para>
  89         Print the <application>pg_test_fsync</application> version and exit.
  90        </para>
  91       </listitem>
  92      </varlistentry>
  93
  94      <varlistentry>
  95       <term><option>-?</option></term>
  96       <term><option>--help</option></term>
  97       <listitem>
  98        <para>
  99         Show help about <application>pg_test_fsync</application> command line
 100         arguments, and exit.
 101        </para>
 102       </listitem>
 103      </varlistentry>
 104     </variablelist>
 105    </para>
 106
 107  </refsect1>
 108
 109  <refsect1>
 110   <title>Environment</title>
 111
 112   <para>
 113    The environment variable <envar>PG_COLOR</envar> specifies whether to use
 114    color in diagnostic messages. Possible values are
 115    <literal>always</literal>, <literal>auto</literal> and
 116    <literal>never</literal>.
 117   </para>
 118  </refsect1>
 119
 120  <refsect1>
 121   <title>See Also</title>
 122
 123   <simplelist type="inline">
 124    <member><xref linkend="app-postgres"/></member>
 125   </simplelist>
 126  </refsect1>
 127 </refentry>