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af06aa822d
The ALTER SYSTEM ref page hadn't been held to a very high standard, nor
was the feature well integrated into section 18.1 (parameter setting).
Also, though commit 4c4654afe had improved the structure of 18.1, it also
introduced a lot of poor wording, imprecision, and outright falsehoods.
Try to clean that up.
143 lines
4.1 KiB
Plaintext
143 lines
4.1 KiB
Plaintext
<!--
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doc/src/sgml/ref/alter_system.sgml
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PostgreSQL documentation
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-->
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<refentry id="SQL-ALTERSYSTEM">
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<indexterm zone="sql-altersystem">
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<primary>ALTER SYSTEM</primary>
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</indexterm>
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<refmeta>
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<refentrytitle>ALTER SYSTEM</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>ALTER SYSTEM</refname>
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<refpurpose>change a server configuration parameter</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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ALTER SYSTEM SET <replaceable class="PARAMETER">configuration_parameter</replaceable> { TO | = } { <replaceable class="PARAMETER">value</replaceable> | '<replaceable class="PARAMETER">value</replaceable>' | DEFAULT }
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ALTER SYSTEM RESET <replaceable class="PARAMETER">configuration_parameter</replaceable>
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ALTER SYSTEM RESET ALL
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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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<command>ALTER SYSTEM</command> is used for changing server configuration
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parameters across the entire database cluster. It can be more convenient
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than the traditional method of manually editing
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the <filename>postgresql.conf</filename> file.
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<command>ALTER SYSTEM</command> writes the given parameter setting to
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the <filename>postgresql.auto.conf</filename> file, which is read in
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addition to <filename>postgresql.conf</filename>.
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Setting a parameter to <literal>DEFAULT</literal>, or using the
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<command>RESET</command> variant, removes that configuration entry from the
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<filename>postgresql.auto.conf</filename> file. Use <literal>RESET
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ALL</literal> to remove all such configuration entries.
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</para>
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<para>
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Values set with <command>ALTER SYSTEM</command> will be effective after
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the next server configuration reload (<systemitem>SIGHUP</>
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or <literal>pg_ctl reload</>), or after the next server restart in the
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case of parameters that can only be changed at server start.
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</para>
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<para>
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Only superusers can use <command>ALTER SYSTEM</command>. Also, since
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this command acts directly on the file system and cannot be rolled back,
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it is not allowed inside a transaction block or function.
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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><replaceable class="parameter">configuration_parameter</replaceable></term>
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<listitem>
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<para>
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Name of a settable configuration parameter. Available parameters are
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documented in <xref linkend="runtime-config">.
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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">value</replaceable></term>
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<listitem>
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<para>
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New value of the parameter. Values can be specified as string
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constants, identifiers, numbers, or comma-separated lists of
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these, as appropriate for the particular parameter.
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<literal>DEFAULT</literal> can be written to specify removing the
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parameter and its value from <filename>postgresql.auto.conf</filename>.
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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>Notes</title>
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<para>
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This command can't be used to set <xref linkend="guc-data-directory">,
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nor parameters that are not allowed in <filename>postgresql.conf</>
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(e.g., <link linkend="runtime-config-preset">preset options</>).
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</para>
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<para>
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See <xref linkend="config-setting"> for other ways to set the parameters.
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</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>
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Set the <literal>wal_level</>:
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<programlisting>
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ALTER SYSTEM SET wal_level = hot_standby;
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</programlisting>
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</para>
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<para>
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Undo that, restoring whatever setting was effective
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in <filename>postgresql.conf</>:
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<programlisting>
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ALTER SYSTEM RESET wal_level;
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</programlisting>
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</para>
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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>ALTER SYSTEM</command> statement is a
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<productname>PostgreSQL</productname> extension.
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</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="SQL-SET"></member>
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<member><xref linkend="SQL-SHOW"></member>
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</simplelist>
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</refsect1>
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</refentry>
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