a commit is
   implicitly performed at the end of the statement (if execution was
   successful, otherwise a rollback is done).
  </para>

  <para>
   Statements are executed more quickly in a transaction block, because
   transaction start/commit requires significant CPU and disk
   activity. Execution of multiple statements inside a transaction is
   also useful to ensure consistency when making several related changes:
   other sessions will be unable to see the intermediate states
   wherein not all the related updates have been done.
  </para>

  <para>
   If the isolation level, read/write mode, or deferrable mode is specified, the new
   transaction has those characteristics, as if
   <link linkend="sql-set-transaction"><command>SET TRANSACTION</command></link>
   was executed.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><literal>WORK</literal></term>
    <term><literal>TRANSACTION</literal></term>
    <listitem>
     <para>
      Optional key words. They have no effect.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>

  <para>
   Refer to <xref linkend="sql-set-transaction"/> for information on the meaning
   of the other parameters to this statement.
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   <link linkend="sql-start-transaction"><command>START TRANSACTION</command></link> has the same functionality
   as <command>BEGIN</command>.
  </para>

  <para>
   Use <link linkend="sql-commit"><command>COMMIT</command></link> or
   <link linkend="sql-rollback"><command>ROLLBACK</command></link>
   to terminate a transaction block.
  </para>

  <para>
   Issuing <command>BEGIN</command> when already inside a transaction block will
   provoke a warning message.  The state of the transaction is not affected.
   To nest transactions within a transaction block, use savepoints
   (see <xref linkend="sql-savepoint"/>).
  </para>

  <para>
   For reasons of backwards compatibility, the commas between successive
   <replaceable class="parameter">transaction_modes</replaceable> can be
   omitted.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   To begin a transaction block:

<programlisting>
BEGIN;
</programlisting></para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>BEGIN</command> is a <productname>PostgreSQL</productname>
   language extension.  It is equivalent to the SQL-standard command
   <link linkend="sql-start-transaction"><command>START TRANSACTION</command></link>, whose reference page
   contains additional compatibility information.
  </para>

  <para>
   The <literal>DEFERRABLE</literal>
   <replaceable class="parameter">transaction_mode</replaceable>
   is a <productname>PostgreSQL</productname> language extension.
  </para>

  <para>
   Incidentally, the <literal>BEGIN</literal> key word is used for a
   different purpose in embedded SQL. You are advised to be careful
   about the transaction semantics when porting database applications.
  </para>
 </refsect1>

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

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