a subtransaction ID.
</para></entry>
</row>
+
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>pg_get_multixact_members</primary>
+ </indexterm>
+ <function>pg_get_multixact_members</function> ( <parameter>multixid</parameter> <type>xid</type> )
+ <returnvalue>setof record</returnvalue>
+ ( <parameter>xid</parameter> <type>xid</type>,
+ <parameter>mode</parameter> <type>text</type> )
+ </para>
+ <para>
+ Returns the transaction ID and lock mode for each member of the
+ specified multixact ID. The lock modes <literal>forupd</literal>,
+ <literal>fornokeyupd</literal>, <literal>sh</literal>, and
+ <literal>keysh</literal> correspond to the row-level locks
+ <literal>FOR UPDATE</literal>, <literal>FOR NO KEY UPDATE</literal>,
+ <literal>FOR SHARE</literal>, and <literal>FOR KEY SHARE</literal>,
+ respectively, as described in <xref linkend="locking-rows"/>. Two
+ additional modes are specific to multixacts:
+ <literal>nokeyupd</literal>, used by updates that do not modify key
+ columns, and <literal>upd</literal>, used by updates or deletes that
+ modify key columns.
+ </para></entry>
+ </row>
</tbody>
</tgroup>
</table>
The internal transaction ID type <type>xid</type> is 32 bits wide and
wraps around every 4 billion transactions. However,
the functions shown in <xref linkend="functions-pg-snapshot"/>, except
- <function>age</function> and <function>mxid_age</function>, use a
+ <function>age</function>, <function>mxid_age</function>, and
+ <function>pg_get_multixact_members</function>, use a
64-bit type <type>xid8</type> that does not wrap around during the life
of an installation, and can be converted to <type>xid</type> by casting if
required. The data type <type>pg_snapshot</type> stores information about
careful aging management, storage cleanup, and wraparound handling.
There is a separate storage area which holds the list of members in
each multixact, which also uses a 32-bit counter and which must also
- be managed.
+ be managed. The system function
+ <function>pg_get_multixact_members()</function> described in
+ <xref linkend="functions-pg-snapshot"/> can be used to examine the
+ transaction IDs associated with a multixact ID.
</para>
<para>