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+<!-- doc/src/sgml/oldsnapshot.sgml -->
+
+<sect1 id="oldsnapshot" xreflabel="old_snapshot">
+ <title>old_snapshot</title>
+
+ <indexterm zone="oldsnapshot">
+  <primary>old_snapshot</primary>
+ </indexterm>
+
+ <para>
+  The <filename>old_snapshot</filename> module allows inspection
+  of the server state that is used to implement
+  <xref linkend="guc-old-snapshot-threshold" />.
+ </para>
+
+ <sect2>
+  <title>Functions</title>
+
+  <variablelist>
+   <varlistentry>
+    <term><function>pg_old_snapshot_time_mapping(array_offset OUT int4, end_timestamp OUT timestamptz, newest_xmin OUT xid) returns setof record</function></term>
+    <listitem>
+     <para>
+      Returns all of the entries in the server's timestamp to XID mapping.
+      Each entry represents the newest xmin of any snapshot taken in the
+      corresponding minute.
+     </para>
+    </listitem>
+   </varlistentry>
+  </variablelist>
+ </sect2>
+
+</sect1>