<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/checkpoint.sgml,v 1.6 2002/04/21 19:02:39 thomas Exp $ -->

<refentry id="sql-checkpoint">
 <refmeta>
  <refentrytitle id="sql-checkpoint-title">CHECKPOINT</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>CHECKPOINT</refname>
  <refpurpose>force a transaction log checkpoint</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
CHECKPOINT
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   Write-Ahead Logging (WAL) puts a checkpoint in the transaction log
   every so often. (To adjust the automatic checkpoint interval, see
   the run-time
   configuration options <parameter>CHECKPOINT_SEGMENTS</parameter>
   and <parameter>CHECKPOINT_TIMEOUT</parameter>.)
   The <command>CHECKPOINT</command> command forces an immediate checkpoint
   when the command is issued, without waiting for a scheduled checkpoint.
  </para>

  <para>
   A checkpoint is a point in the transaction log sequence at which
   all data files have been updated to reflect the information in the
   log.  All data files will be flushed to disk.  Refer to the
   <citetitle>PostgreSQL Administrator's Guide</citetitle> for more
   information about the WAL system.
  </para>

  <para>
   Only superusers may call <command>CHECKPOINT</command>.  The command is
   not intended for use during normal operation.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <para>
   <citetitle>PostgreSQL Administrator's Guide</citetitle>
  </para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   The <command>CHECKPOINT</command> command is a
   <productname>PostgreSQL</productname> language extension.
  </para>
 </refsect1>
</refentry>
