xlogdirtywrite_v4.diff

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index b4fcbaf..0ae885b 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1907,6 +1907,13 @@ include 'filename'
         results in most cases.
        </para>
 
+       <para>
+        When you see pg_stat_walwriter.dirty_write, which means number
+        of buffer flushing at buffer full, is continuously increasing
+        in your running server, you may need to enlarge this buffer
+        size.
+       </para>
+
       </listitem>
      </varlistentry>
 
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 39ccfbb..3117f91 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -278,6 +278,14 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
      </row>
 
      <row>
+      <entry><structname>pg_stat_walwriter</><indexterm><primary>pg_stat_walwriter</primary></indexterm></entry>
+      <entry>One row only, showing statistics about the wal writer
+       process's activity. See <xref linkend="pg-stat-walwriter-view">
+       for details.
+     </entry>
+     </row>
+
+     <row>
       <entry><structname>pg_stat_database</><indexterm><primary>pg_stat_database</primary></indexterm></entry>
       <entry>One row per database, showing database-wide statistics. See
        <xref linkend="pg-stat-database-view"> for details.
@@ -735,6 +743,39 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
    single row, containing global data for the cluster.
   </para>
 
+  <table id="pg-stat-walwriter-view" xreflabel="pg_stat_walwriter">
+   <title><structname>pg_stat_walwriter</structname> View</title>
+
+   <tgroup cols="3">
+    <thead>
+    <row>
+      <entry>Column</entry>
+      <entry>Type</entry>
+      <entry>Description</entry>
+     </row>
+    </thead>
+
+    <tbody>
+     <row>
+      <entry><structfield>dirty_writes</></entry>
+      <entry><type>bigint</type></entry>
+      <entry>Number of dirty writes, which means flushing wal buffers
+       because of its full.</entry>
+     </row>
+     <row>
+      <entry><structfield>stats_reset</></entry>
+      <entry><type>timestamp with time zone</type></entry>
+      <entry>Time at which these statistics were last reset</entry>
+     </row>
+    </tbody>
+    </tgroup>
+  </table>
+
+  <para>
+   The <structname>pg_stat_walwriter</structname> view will always have a
+   single row, containing global data for the cluster.
+  </para>
+
   <table id="pg-stat-database-view" xreflabel="pg_stat_database">
    <title><structname>pg_stat_database</structname> View</title>
    <tgroup cols="3">
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index d251d08..631a0af 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -1347,6 +1347,7 @@ AdvanceXLInsertBuffer(bool new_segment)
 				WriteRqst.Write = OldPageRqstPtr;
 				WriteRqst.Flush = 0;
 				XLogWrite(WriteRqst, false, false);
+				WalWriterStats.m_xlog_dirty_writes++;
 				LWLockRelease(WALWriteLock);
 				TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
 			}
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 607a72f..40f0c34 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -671,6 +671,11 @@ CREATE VIEW pg_stat_bgwriter AS
         pg_stat_get_buf_alloc() AS buffers_alloc,
         pg_stat_get_bgwriter_stat_reset_time() AS stats_reset;
 
+CREATE VIEW pg_stat_walwriter AS
+    SELECT
+        pg_stat_get_xlog_dirty_writes() AS dirty_writes,
+        pg_stat_get_wal_stat_reset_time() AS stats_reset;
+
 CREATE VIEW pg_user_mappings AS
     SELECT
         U.oid       AS umid,
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index be3adf1..5be78c6 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -125,6 +125,15 @@ char	   *pgstat_stat_tmpname = NULL;
  */
 PgStat_MsgBgWriter BgWriterStats;
 
+/*
+ * WalWriter global statistics counter.
+ * Despite its name, this counter is actually used not only in walwriter,
+ * but also in each backend process to sum up xlog dirty writes.
+ * Those processes would increment this counter in each XLogWrite call,
+ * then send it to the stat collector process.
+ */
+PgStat_MsgWalWriter WalWriterStats;
+
 /* ----------
  * Local data
  * ----------
@@ -279,6 +288,7 @@ static void pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len);
 static void pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len);
 static void pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len);
 static void pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len);
+static void pgstat_recv_walwriter(PgStat_MsgWalWriter *msg, int len);
 static void pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len);
 static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);
 static void pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len);
@@ -762,6 +772,9 @@ pgstat_report_stat(bool force)
 
 	/* Now, send function statistics */
 	pgstat_send_funcstats();
+
+	/* Now, send wal buffer flush statistics */
+	pgstat_send_walwriter();
 }
 
 /*
@@ -1188,11 +1201,13 @@ pgstat_reset_shared_counters(const char *target)
 
 	if (strcmp(target, "bgwriter") == 0)
 		msg.m_resettarget = RESET_BGWRITER;
+	else if (strcmp(target, "walwriter") == 0)
+		msg.m_resettarget = RESET_WALWRITER;
 	else
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("unrecognized reset target: \"%s\"", target),
-				 errhint("Target must be \"bgwriter\".")));
+				 errhint("Target must be \"bgwriter\" or \"walwriter\".")));
 
 	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
 	pgstat_send(&msg, sizeof(msg));
@@ -2988,6 +3003,38 @@ pgstat_send_bgwriter(void)
 	MemSet(&BgWriterStats, 0, sizeof(BgWriterStats));
 }
 
+/* ----------
+ * pgstat_send_walwriter() -
+ *
+ *		Send walwriter statistics to the collector
+ * ----------
+ */
+void
+pgstat_send_walwriter(void)
+{
+	/* We assume this initializes to zeroes */
+	static const PgStat_MsgBgWriter all_zeroes;
+
+	/*
+	 * This function can be called even if nothing at all has happened. In
+	 * this case, avoid sending a completely empty message to the stats
+	 * collector.
+	 */
+	if (memcmp(&WalWriterStats, &all_zeroes, sizeof(PgStat_MsgWalWriter)) == 0)
+		return;
+
+	/*
+	 * Prepare and send the message
+	 */
+	pgstat_setheader(&WalWriterStats.m_hdr, PGSTAT_MTYPE_WALWRITER);
+	pgstat_send(&WalWriterStats, sizeof(WalWriterStats));
+
+	/*
+	 * Clear out the statistics buffer, so it can be re-used.
+	 */
+	MemSet(&WalWriterStats, 0, sizeof(WalWriterStats));
+}
+
 
 /* ----------
  * PgstatCollectorMain() -
@@ -3209,6 +3256,10 @@ PgstatCollectorMain(int argc, char *argv[])
 					pgstat_recv_bgwriter((PgStat_MsgBgWriter *) &msg, len);
 					break;
 
+				case PGSTAT_MTYPE_WALWRITER:
+					pgstat_recv_walwriter((PgStat_MsgWalWriter *) &msg, len);
+					break;
+
 				case PGSTAT_MTYPE_FUNCSTAT:
 					pgstat_recv_funcstat((PgStat_MsgFuncstat *) &msg, len);
 					break;
@@ -3638,7 +3689,8 @@ pgstat_read_statsfile(Oid onlydb, bool permanent)
 	 * Set the current timestamp (will be kept only in case we can't load an
 	 * existing statsfile).
 	 */
-	globalStats.stat_reset_timestamp = GetCurrentTimestamp();
+	globalStats.stat_bgw_reset_timestamp = GetCurrentTimestamp();
+	globalStats.stat_wal_reset_timestamp = GetCurrentTimestamp();
 
 	/*
 	 * Try to open the status file. If it doesn't exist, the backends simply
@@ -4381,8 +4433,23 @@ pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
 	if (msg->m_resettarget == RESET_BGWRITER)
 	{
 		/* Reset the global background writer statistics for the cluster. */
-		memset(&globalStats, 0, sizeof(globalStats));
-		globalStats.stat_reset_timestamp = GetCurrentTimestamp();
+		globalStats.timed_checkpoints       = 0;
+		globalStats.requested_checkpoints   = 0;
+		globalStats.checkpoint_write_time   = 0;
+		globalStats.checkpoint_sync_time    = 0;
+		globalStats.buf_written_checkpoints = 0;
+		globalStats.buf_written_clean       = 0;
+		globalStats.maxwritten_clean        = 0;
+		globalStats.buf_written_backend     = 0;
+		globalStats.buf_fsync_backend       = 0;
+		globalStats.buf_alloc               = 0;
+		globalStats.stat_bgw_reset_timestamp = GetCurrentTimestamp();
+	}
+	else if (msg->m_resettarget == RESET_WALWRITER)
+	{
+		/* Reset the global walwriter statistics for the cluster. */
+		globalStats.xlog_dirty_writes = 0;
+		globalStats.stat_wal_reset_timestamp = GetCurrentTimestamp();
 	}
 
 	/*
@@ -4536,6 +4603,18 @@ pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len)
 }
 
 /* ----------
+ * pgstat_recv_walwriter() -
+ *
+ *	Process a WALWRITER message.
+ * ----------
+ */
+static void
+pgstat_recv_walwriter(PgStat_MsgWalWriter *msg, int len)
+{
+	globalStats.xlog_dirty_writes += msg->m_xlog_dirty_writes;
+}
+
+/* ----------
  * pgstat_recv_recoveryconflict() -
  *
  *	Process a RECOVERYCONFLICT message.
diff --git a/src/backend/postmaster/walwriter.c b/src/backend/postmaster/walwriter.c
index c3e15ef..cd294fb 100644
--- a/src/backend/postmaster/walwriter.c
+++ b/src/backend/postmaster/walwriter.c
@@ -290,6 +290,8 @@ WalWriterMain(void)
 		else if (left_till_hibernate > 0)
 			left_till_hibernate--;
 
+		pgstat_send_walwriter();
+
 		/*
 		 * Sleep until we are signaled or WalWriterDelay has elapsed.  If we
 		 * haven't done anything useful for quite some time, lengthen the
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 7d4059f..fc25dda 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -97,6 +97,7 @@ extern Datum pg_stat_get_bgwriter_stat_reset_time(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_buf_written_backend(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_buf_fsync_backend(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_buf_alloc(PG_FUNCTION_ARGS);
+extern Datum pg_stat_get_wal_stat_reset_time(PG_FUNCTION_ARGS);
 
 extern Datum pg_stat_get_xact_numscans(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_xact_tuples_returned(PG_FUNCTION_ARGS);
@@ -118,6 +119,8 @@ extern Datum pg_stat_reset_shared(PG_FUNCTION_ARGS);
 extern Datum pg_stat_reset_single_table_counters(PG_FUNCTION_ARGS);
 extern Datum pg_stat_reset_single_function_counters(PG_FUNCTION_ARGS);
 
+extern Datum pg_stat_get_xlog_dirty_writes(PG_FUNCTION_ARGS);
+
 /* Global bgwriter statistics, from bgwriter.c */
 extern PgStat_MsgBgWriter bgwriterStats;
 
@@ -1443,7 +1446,7 @@ pg_stat_get_checkpoint_sync_time(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_bgwriter_stat_reset_time(PG_FUNCTION_ARGS)
 {
-	PG_RETURN_TIMESTAMPTZ(pgstat_fetch_global()->stat_reset_timestamp);
+	PG_RETURN_TIMESTAMPTZ(pgstat_fetch_global()->stat_bgw_reset_timestamp);
 }
 
 Datum
@@ -1465,6 +1468,12 @@ pg_stat_get_buf_alloc(PG_FUNCTION_ARGS)
 }
 
 Datum
+pg_stat_get_wal_stat_reset_time(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_TIMESTAMPTZ(pgstat_fetch_global()->stat_wal_reset_timestamp);
+}
+
+Datum
 pg_stat_get_xact_numscans(PG_FUNCTION_ARGS)
 {
 	Oid			relid = PG_GETARG_OID(0);
@@ -1701,3 +1710,9 @@ pg_stat_reset_single_function_counters(PG_FUNCTION_ARGS)
 
 	PG_RETURN_VOID();
 }
+
+Datum
+pg_stat_get_xlog_dirty_writes(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_INT64(pgstat_fetch_global()->xlog_dirty_writes);
+}
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index f935eb1..d6edb5a 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -2702,6 +2702,8 @@ DATA(insert OID = 3063 ( pg_stat_get_buf_fsync_backend PGNSP PGUID 12 1 0 0 0 f
 DESCR("statistics: number of backend buffer writes that did their own fsync");
 DATA(insert OID = 2859 ( pg_stat_get_buf_alloc			PGNSP PGUID 12 1 0 0 0 f f f f t f s 0 0 20 "" _null_ _null_ _null_ _null_ pg_stat_get_buf_alloc _null_ _null_ _null_ ));
 DESCR("statistics: number of buffer allocations");
+DATA(insert OID = 2860 ( pg_stat_get_wal_stat_reset_time PGNSP PGUID 12 1 0 0 0 f f f f t f s 0 0 1184 "" _null_ _null_ _null_ _null_	pg_stat_get_wal_stat_reset_time _null_ _null_ _null_ ));
+DESCR("statistics: last reset for the wal");
 
 DATA(insert OID = 2978 (  pg_stat_get_function_calls		PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 20 "26" _null_ _null_ _null_ _null_ pg_stat_get_function_calls _null_ _null_ _null_ ));
 DESCR("statistics: number of function calls");
@@ -2746,6 +2748,9 @@ DESCR("statistics: reset collected statistics for a single table or index in the
 DATA(insert OID = 3777 (  pg_stat_reset_single_function_counters	PGNSP PGUID 12 1 0 0 0 f f f f f f v 1 0 2278 "26" _null_ _null_ _null_ _null_	pg_stat_reset_single_function_counters _null_ _null_ _null_ ));
 DESCR("statistics: reset collected statistics for a single function in the current database");
 
+DATA(insert OID = 3766 (  pg_stat_get_xlog_dirty_writes  PGNSP PGUID 12 1 0 0 0 f f f f f f v 0 0 20 "" _null_ _null_ _null_ _null_ pg_stat_get_xlog_dirty_writes _null_ _null_ _null_ ));
+DESCR("statistics: get xlog dirty buffer write statistics");
+
 DATA(insert OID = 3163 (  pg_trigger_depth				PGNSP PGUID 12 1 0 0 0 f f f f t f s 0 0 23 "" _null_ _null_ _null_ _null_ pg_trigger_depth _null_ _null_ _null_ ));
 DESCR("current trigger depth");
 
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 613c1c2..f71c538 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -45,6 +45,7 @@ typedef enum StatMsgType
 	PGSTAT_MTYPE_VACUUM,
 	PGSTAT_MTYPE_ANALYZE,
 	PGSTAT_MTYPE_BGWRITER,
+	PGSTAT_MTYPE_WALWRITER,
 	PGSTAT_MTYPE_FUNCSTAT,
 	PGSTAT_MTYPE_FUNCPURGE,
 	PGSTAT_MTYPE_RECOVERYCONFLICT,
@@ -102,7 +103,8 @@ typedef struct PgStat_TableCounts
 /* Possible targets for resetting cluster-wide shared values */
 typedef enum PgStat_Shared_Reset_Target
 {
-	RESET_BGWRITER
+	RESET_BGWRITER,
+	RESET_WALWRITER
 } PgStat_Shared_Reset_Target;
 
 /* Possible object types for resetting single counters */
@@ -372,6 +374,17 @@ typedef struct PgStat_MsgBgWriter
 } PgStat_MsgBgWriter;
 
 /* ----------
+ * PgStat_MsgWalWriter			Sent by the walwriter to update statistics.
+ * ----------
+ */
+typedef struct PgStat_MsgWalWriter
+{
+	PgStat_MsgHdr m_hdr;
+
+	PgStat_Counter m_xlog_dirty_writes;
+} PgStat_MsgWalWriter;
+
+/* ----------
  * PgStat_MsgRecoveryConflict	Sent by the backend upon recovery conflict
  * ----------
  */
@@ -499,6 +512,7 @@ typedef union PgStat_Msg
 	PgStat_MsgVacuum msg_vacuum;
 	PgStat_MsgAnalyze msg_analyze;
 	PgStat_MsgBgWriter msg_bgwriter;
+	PgStat_MsgWalWriter msg_walwriter;
 	PgStat_MsgFuncstat msg_funcstat;
 	PgStat_MsgFuncpurge msg_funcpurge;
 	PgStat_MsgRecoveryConflict msg_recoveryconflict;
@@ -622,7 +636,10 @@ typedef struct PgStat_GlobalStats
 	PgStat_Counter buf_written_backend;
 	PgStat_Counter buf_fsync_backend;
 	PgStat_Counter buf_alloc;
-	TimestampTz stat_reset_timestamp;
+	TimestampTz stat_bgw_reset_timestamp;
+
+	PgStat_Counter xlog_dirty_writes;
+	TimestampTz stat_wal_reset_timestamp;
 } PgStat_GlobalStats;
 
 
@@ -730,6 +747,8 @@ extern char *pgstat_stat_filename;
  */
 extern PgStat_MsgBgWriter BgWriterStats;
 
+extern PgStat_MsgWalWriter WalWriterStats;
+
 /*
  * Updated by pgstat_count_buffer_*_time macros
  */
@@ -858,6 +877,7 @@ extern void pgstat_twophase_postabort(TransactionId xid, uint16 info,
 						  void *recdata, uint32 len);
 
 extern void pgstat_send_bgwriter(void);
+extern void pgstat_send_walwriter(void);
 
 /* ----------
  * Support functions for the SQL-callable functions to