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<!--
doc/src/sgml/ref/alter_system.sgml
PostgreSQL documentation
-->
<refentry id="SQL-ALTERSYSTEM">
<indexterm zone="sql-altersystem">
<primary>ALTER SYSTEM</primary>
</indexterm>
<refmeta>
<refentrytitle>ALTER SYSTEM</refentrytitle>
<manvolnum>7</manvolnum>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>ALTER SYSTEM</refname>
<refpurpose>change a server configuration parameter</refpurpose>
</refnamediv>
<refsynopsisdiv>
<synopsis>
ALTER SYSTEM SET <replaceable class="PARAMETER">configuration_parameter</replaceable> { TO | = } { <replaceable class="PARAMETER">value</replaceable> | '<replaceable class="PARAMETER">value</replaceable>' | DEFAULT }
ALTER SYSTEM RESET <replaceable class="PARAMETER">configuration_parameter</replaceable>
ALTER SYSTEM RESET ALL
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>ALTER SYSTEM</command> writes the configuration parameter
values to the <filename>postgresql.auto.conf</filename> file.
Setting the parameter to <literal>DEFAULT</literal>, or using the
<command>RESET</command> variant, removes the configuration entry from
<filename>postgresql.auto.conf</filename> file. Use <literal>RESET
ALL</literal> to clear all configuration entries. The values will
be effective after reload of server configuration (SIGHUP) or in next
server start based on the type of configuration parameter modified.
</para>
<para>
This command is not allowed inside transaction block or function.
</para>
<para>
See <xref linkend="config-setting"> for other ways to set the parameters and
how they become effective.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="parameter">configuration_parameter</replaceable></term>
<listitem>
<para>
Name of a settable run-time parameter. Available parameters are
documented in <xref linkend="runtime-config">.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">value</replaceable></term>
<listitem>
<para>
New value of parameter. Values can be specified as string
constants, identifiers, numbers, or comma-separated lists of
these, as appropriate for the particular parameter.
<literal>DEFAULT</literal> can be written to specify to remove the
parameter and its value from <filename>postgresql.auto.conf</filename>
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
This command can't be used to set <xref linkend="guc-data-directory">
and any parameters (e.g., <link linkend="runtime-config-preset">preset options</>)
that are not allowed in <filename>postgresql.conf</>.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Set the <literal>wal_level</>:
<programlisting>
ALTER SYSTEM SET wal_level = hot_standby;
</programlisting>
</para>
<para>
Set the <literal>authentication_timeout</>:
<programlisting>
ALTER SYSTEM SET authentication_timeout = 10;
</programlisting></para>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
The <command>ALTER SYSTEM</command> statement is a
<productname>PostgreSQL</productname> extension.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="SQL-SET"></member>
<member><xref linkend="SQL-SHOW"></member>
</simplelist>
</refsect1>
</refentry>
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