doc/src/sgml/ref/release_savepoint.sgml - master - githubmirror/postgres

doc/src/sgml/ref/release_savepoint.sgml
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<!--
doc/src/sgml/ref/release_savepoint.sgml
PostgreSQL documentation
-->

<refentry id="sql-release-savepoint">
 <indexterm zone="sql-release-savepoint">
  <primary>RELEASE SAVEPOINT</primary>
 </indexterm>

 <indexterm zone="sql-release-savepoint">
  <primary>savepoints</primary>
  <secondary>releasing</secondary>
 </indexterm>

 <refmeta>
  <refentrytitle>RELEASE SAVEPOINT</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>RELEASE SAVEPOINT</refname>
  <refpurpose>release a previously defined savepoint</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
RELEASE [ SAVEPOINT ] <replaceable>savepoint_name</replaceable>
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>RELEASE SAVEPOINT</command> releases the named savepoint and
   all active savepoints that were created after the named savepoint,
   and frees their resources.  All changes made since the creation of
   the savepoint that didn't already get rolled back are merged into
   the transaction or savepoint that was active when the named savepoint
   was created.  Changes made after <command>RELEASE SAVEPOINT</command>
   will also be part of this active transaction or savepoint.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable>savepoint_name</replaceable></term>
    <listitem>
     <para>
      The name of the savepoint to release.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   Specifying a savepoint name that was not previously defined is an error.
  </para>

  <para>
   It is not possible to release a savepoint when the transaction is in
   an aborted state;  to do that, use <xref linkend="sql-rollback-to"/>.
  </para>

  <para>
   If multiple savepoints have the same name, only the most recently defined
   unreleased one is released.  Repeated commands will release progressively
   older savepoints.
  </para>

 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   To establish and later release a savepoint:
<programlisting>
BEGIN;
    INSERT INTO table1 VALUES (3);
    SAVEPOINT my_savepoint;
    INSERT INTO table1 VALUES (4);
    RELEASE SAVEPOINT my_savepoint;
COMMIT;
</programlisting>
   The above transaction will insert both 3 and 4.
  </para>

  <para>
   A more complex example with multiple nested subtransactions:
<programlisting>
BEGIN;
    INSERT INTO table1 VALUES (1);
    SAVEPOINT sp1;
    INSERT INTO table1 VALUES (2);
    SAVEPOINT sp2;
    INSERT INTO table1 VALUES (3);
    RELEASE SAVEPOINT sp2;
    INSERT INTO table1 VALUES (4))); -- generates an error
</programlisting>
   In this example, the application requests the release of the savepoint
   <literal>sp2</literal>, which inserted 3.  This changes the insert's
   transaction context to <literal>sp1</literal>.  When the statement
   attempting to insert value 4 generates an error, the insertion of 2 and
   4 are lost because they are in the same, now-rolled back savepoint,
   and value 3 is in the same transaction context.  The application can
   now only choose one of these two commands, since all other commands
   will be ignored:
<programlisting>
ROLLBACK;
ROLLBACK TO SAVEPOINT sp1;
</programlisting>
   Choosing <command>ROLLBACK</command> will abort everything, including
   value 1, whereas <command>ROLLBACK TO SAVEPOINT sp1</command> will retain
   value 1 and allow the transaction to continue.
  </para>

 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   This command conforms to the <acronym>SQL</acronym> standard.  The standard
   specifies that the key word <literal>SAVEPOINT</literal> is
   mandatory, but <productname>PostgreSQL</productname> allows it to
   be omitted.
  </para>
 </refsect1>

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

  <simplelist type="inline">
   <member><xref linkend="sql-begin"/></member>
   <member><xref linkend="sql-commit"/></member>
   <member><xref linkend="sql-rollback"/></member>
   <member><xref linkend="sql-rollback-to"/></member>
   <member><xref linkend="sql-savepoint"/></member>
  </simplelist>
 </refsect1>
</refentry>