Add monitoring function pg_last_xact_replay_timestamp.

Fujii Masao, with a little wordsmithing by me.

Author: robertmhaas

doc/src/sgml/func.sgml

@@ -13551,6 +13551,9 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
    <indexterm>
     <primary>pg_last_xlog_replay_location</primary>
    </indexterm>
+   <indexterm>
+    <primary>pg_last_xact_replay_timestamp</primary>
+   </indexterm>
 
    <para>
     The functions shown in <xref
@@ -13605,6 +13608,22 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
         the function returns NULL.
        </entry>
       </row>
+      <row>
+       <entry>
+        <literal><function>pg_last_xact_replay_timestamp()</function></literal>
+        </entry>
+       <entry><type>timestamp with time zone</type></entry>
+       <entry>Get timestamp of last transaction replayed during recovery.
+        This is the time at which the commit or abort WAL record for that
+        transaction was generated.
+        If no transactions have been replayed during recovery, this function
+        returns NULL.  Otherwise, if recovery is still in progress this will
+        increase monotonically.  If recovery has completed then this value will
+        remain static at the value of the last transaction applied during that
+        recovery.  When the server has been started normally without recovery
+        the function returns NULL.
+       </entry>
+      </row>
      </tbody>
     </tgroup>
    </table>

src/backend/access/transam/xlog.c

@@ -5604,6 +5604,24 @@ GetLatestXTime(void)
 	return xtime;
 }
 
+/*
+ * Returns timestamp of latest processed commit/abort record.
+ *
+ * When the server has been started normally without recovery the function
+ * returns NULL. 
+ */
+Datum
+pg_last_xact_replay_timestamp(PG_FUNCTION_ARGS)
+{
+	TimestampTz	xtime;
+
+	xtime = GetLatestXTime();
+	if (xtime == 0)
+		PG_RETURN_NULL();
+
+	PG_RETURN_TIMESTAMPTZ(xtime);
+}
+
 /*
  * Returns bool with current recovery mode, a global state.
  */

src/include/access/xlog_internal.h

@@ -271,6 +271,7 @@ extern Datum pg_current_xlog_location(PG_FUNCTION_ARGS);
 extern Datum pg_current_xlog_insert_location(PG_FUNCTION_ARGS);
 extern Datum pg_last_xlog_receive_location(PG_FUNCTION_ARGS);
 extern Datum pg_last_xlog_replay_location(PG_FUNCTION_ARGS);
+extern Datum pg_last_xact_replay_timestamp(PG_FUNCTION_ARGS);
 extern Datum pg_xlogfile_name_offset(PG_FUNCTION_ARGS);
 extern Datum pg_xlogfile_name(PG_FUNCTION_ARGS);
 extern Datum pg_is_in_recovery(PG_FUNCTION_ARGS);

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201010301
+#define CATALOG_VERSION_NO	201011091
 
 #endif

src/include/catalog/pg_proc.h

@@ -3383,6 +3383,8 @@ DATA(insert OID = 3820 ( pg_last_xlog_receive_location	PGNSP PGUID 12 1 0 0 f f
 DESCR("current xlog flush location");
 DATA(insert OID = 3821 ( pg_last_xlog_replay_location	PGNSP PGUID 12 1 0 0 f f f t f v 0 0 25 "" _null_ _null_ _null_ _null_ pg_last_xlog_replay_location _null_ _null_ _null_ ));
 DESCR("last xlog replay location");
+DATA(insert OID = 3830 ( pg_last_xact_replay_timestamp	PGNSP PGUID 12 1 0 0 f f f t f v 0 0 1184 "" _null_ _null_ _null_ _null_ pg_last_xact_replay_timestamp _null_ _null_ _null_ ));
+DESCR("timestamp of last replay xact");
 
 DATA(insert OID = 2621 ( pg_reload_conf			PGNSP PGUID 12 1 0 0 f f f t f v 0 0 16 "" _null_ _null_ _null_ _null_ pg_reload_conf _null_ _null_ _null_ ));
 DESCR("reload configuration files");