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<!--
doc/src/sgml/ref/checkpoint.sgml
PostgreSQL documentation
-->
<refentry id="sql-checkpoint">
<indexterm zone="sql-checkpoint">
<primary>CHECKPOINT</primary>
</indexterm>
<refmeta>
<refentrytitle>CHECKPOINT</refentrytitle>
<manvolnum>7</manvolnum>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>CHECKPOINT</refname>
<refpurpose>force a write-ahead log checkpoint</refpurpose>
</refnamediv>
<refsynopsisdiv>
<synopsis>
CHECKPOINT [ ( option [, ...] ) ]
<phrase>where <replaceable class="parameter">option</replaceable> can be one of:</phrase>
FLUSH_UNLOGGED [ <replaceable class="parameter">boolean</replaceable> ]
MODE { FAST | SPREAD }
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
A checkpoint is a point in the write-ahead 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
<xref linkend="wal-configuration"/> for more details about what happens
during a checkpoint.
</para>
<para>
By default, the <command>CHECKPOINT</command> command forces a fast
checkpoint when the command is issued, without waiting for a
regular checkpoint scheduled by the system (controlled by the settings in
<xref linkend="runtime-config-wal-checkpoints"/>).
To request the checkpoint be spread over a longer interval, set the
<literal>MODE</literal> option to <literal>SPREAD</literal>.
<command>CHECKPOINT</command> is not intended for use during normal
operation.
</para>
<para>
The server may consolidate concurrently requested checkpoints. Such
consolidated requests will contain a combined set of options. For example,
if one session requests a fast checkpoint and another requests a spread
checkpoint, the server may combine those requests and perform one fast
checkpoint.
</para>
<para>
If executed during recovery, the <command>CHECKPOINT</command> command
will force a restartpoint (see <xref linkend="wal-configuration"/>)
rather than writing a new checkpoint.
</para>
<para>
Only superusers or users with the privileges of
the <xref linkend="predefined-role-pg-checkpoint"/>
role can call <command>CHECKPOINT</command>.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><literal>FLUSH_UNLOGGED</literal></term>
<listitem>
<para>
Normally, <command>CHECKPOINT</command> does not flush dirty buffers of
unlogged relations. This option, which is disabled by default, enables
flushing unlogged relations to disk.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>MODE</literal></term>
<listitem>
<para>
When set to <literal>FAST</literal>, which is the default, the requested
checkpoint will be completed as fast as possible, which may result in a
significantly higher rate of I/O during the checkpoint.
</para>
<para>
<literal>MODE</literal> can also be set to <literal>SPREAD</literal> to
request the checkpoint be spread over a longer interval (controlled via
the settings in <xref linkend="runtime-config-wal-checkpoints"/>), like a
regular checkpoint scheduled by the system. This can reduce the rate of
I/O during the checkpoint.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">boolean</replaceable></term>
<listitem>
<para>
Specifies whether the selected option should be turned on or off.
You can write <literal>TRUE</literal>, <literal>ON</literal>, or
<literal>1</literal> to enable the option, and <literal>FALSE</literal>,
<literal>OFF</literal>, or <literal>0</literal> to disable it. The
<replaceable class="parameter">boolean</replaceable> value can also
be omitted, in which case <literal>TRUE</literal> is assumed.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
The <command>CHECKPOINT</command> command is a
<productname>PostgreSQL</productname> language extension.
</para>
</refsect1>
</refentry>
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