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This option, which is disabled by default, can be used to request the checkpoint also flush dirty buffers of unlogged relations. As with the MODE option, the server may consolidate the options for concurrently requested checkpoints. For example, if one session uses (FLUSH_UNLOGGED FALSE) and another uses (FLUSH_UNLOGGED TRUE), the server may perform one checkpoint with FLUSH_UNLOGGED enabled. Author: Christoph Berg <myon@debian.org> Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at> Reviewed-by: Fujii Masao <masao.fujii@oss.nttdata.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Discussion: https://postgr.es/m/aDnaKTEf-0dLiEfz%40msg.df7cb.de
134 lines
4.2 KiB
Plaintext
134 lines
4.2 KiB
Plaintext
<!--
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doc/src/sgml/ref/checkpoint.sgml
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PostgreSQL documentation
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-->
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<refentry id="sql-checkpoint">
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<indexterm zone="sql-checkpoint">
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<primary>CHECKPOINT</primary>
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</indexterm>
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<refmeta>
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<refentrytitle>CHECKPOINT</refentrytitle>
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<manvolnum>7</manvolnum>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>CHECKPOINT</refname>
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<refpurpose>force a write-ahead log checkpoint</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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CHECKPOINT [ ( option [, ...] ) ]
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<phrase>where <replaceable class="parameter">option</replaceable> can be one of:</phrase>
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FLUSH_UNLOGGED [ <replaceable class="parameter">boolean</replaceable> ]
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MODE { FAST | SPREAD }
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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A checkpoint is a point in the write-ahead log sequence at which
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all data files have been updated to reflect the information in the
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log. All data files will be flushed to disk. Refer to
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<xref linkend="wal-configuration"/> for more details about what happens
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during a checkpoint.
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</para>
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<para>
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By default, the <command>CHECKPOINT</command> command forces a fast
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checkpoint when the command is issued, without waiting for a
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regular checkpoint scheduled by the system (controlled by the settings in
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<xref linkend="runtime-config-wal-checkpoints"/>).
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To request the checkpoint be spread over a longer interval, set the
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<literal>MODE</literal> option to <literal>SPREAD</literal>.
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<command>CHECKPOINT</command> is not intended for use during normal
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operation.
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</para>
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<para>
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The server may consolidate concurrently requested checkpoints. Such
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consolidated requests will contain a combined set of options. For example,
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if one session requests a fast checkpoint and another requests a spread
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checkpoint, the server may combine those requests and perform one fast
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checkpoint.
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</para>
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<para>
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If executed during recovery, the <command>CHECKPOINT</command> command
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will force a restartpoint (see <xref linkend="wal-configuration"/>)
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rather than writing a new checkpoint.
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</para>
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<para>
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Only superusers or users with the privileges of
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the <xref linkend="predefined-role-pg-checkpoint"/>
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role can call <command>CHECKPOINT</command>.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><literal>FLUSH_UNLOGGED</literal></term>
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<listitem>
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<para>
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Normally, <command>CHECKPOINT</command> does not flush dirty buffers of
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unlogged relations. This option, which is disabled by default, enables
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flushing unlogged relations to disk.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>MODE</literal></term>
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<listitem>
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<para>
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When set to <literal>FAST</literal>, which is the default, the requested
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checkpoint will be completed as fast as possible, which may result in a
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significantly higher rate of I/O during the checkpoint.
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</para>
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<para>
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<literal>MODE</literal> can also be set to <literal>SPREAD</literal> to
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request the checkpoint be spread over a longer interval (controlled via
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the settings in <xref linkend="runtime-config-wal-checkpoints"/>), like a
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regular checkpoint scheduled by the system. This can reduce the rate of
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I/O during the checkpoint.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">boolean</replaceable></term>
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<listitem>
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<para>
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Specifies whether the selected option should be turned on or off.
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You can write <literal>TRUE</literal>, <literal>ON</literal>, or
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<literal>1</literal> to enable the option, and <literal>FALSE</literal>,
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<literal>OFF</literal>, or <literal>0</literal> to disable it. The
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<replaceable class="parameter">boolean</replaceable> value can also
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be omitted, in which case <literal>TRUE</literal> is assumed.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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The <command>CHECKPOINT</command> command is a
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<productname>PostgreSQL</productname> language extension.
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</para>
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</refsect1>
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</refentry>
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