xlogdirtywrite_v3.diff

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index ff56c26..234d568 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -1518,6 +1518,7 @@ 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/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 8389d5c..f031be1 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);
@@ -1188,6 +1198,8 @@ 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),
@@ -2988,6 +3000,38 @@ 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() -
@@ -3207,6 +3251,10 @@ 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;
@@ -4382,6 +4430,12 @@ pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
 		memset(&globalStats, 0, sizeof(globalStats));
 		globalStats.stat_reset_timestamp = GetCurrentTimestamp();
 	}
+	else if (msg->m_resettarget == RESET_WALWRITER)
+	{
+		/* Reset the global walwriter statistics for the cluster. */
+		memset(&globalStats, 0, sizeof(globalStats));
+		globalStats.stat_reset_timestamp = GetCurrentTimestamp();
+	}
 
 	/*
 	 * Presumably the sender of this message validated the target, don't
@@ -4534,6 +4588,18 @@ 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 4313901..6fbc5f9 100644
--- a/src/backend/postmaster/walwriter.c
+++ b/src/backend/postmaster/walwriter.c
@@ -289,6 +289,8 @@ 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/tcop/postgres.c b/src/backend/tcop/postgres.c
index f1248a8..1ed2c0a 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3918,6 +3918,8 @@ PostgresMain(int argc, char *argv[], const char *username)
 				pgstat_report_activity(STATE_IDLE, NULL);
 			}
 
+			pgstat_send_walwriter();
+
 			ReadyForQuery(whereToSendOutput);
 			send_ready_for_query = false;
 		}
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 7d4059f..f707c9a 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -118,6 +118,8 @@ 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;
 
@@ -1701,3 +1703,9 @@ 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 77a3b41..da2225c 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -2740,6 +2740,9 @@ 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..59aa1ba 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;
@@ -622,6 +636,7 @@ typedef struct PgStat_GlobalStats
 	PgStat_Counter buf_written_backend;
 	PgStat_Counter buf_fsync_backend;
 	PgStat_Counter buf_alloc;
+	PgStat_Counter xlog_dirty_writes;
 	TimestampTz stat_reset_timestamp;
 } PgStat_GlobalStats;
 
@@ -730,6 +745,8 @@ extern char *pgstat_stat_filename;
  */
 extern PgStat_MsgBgWriter BgWriterStats;
 
+extern PgStat_MsgWalWriter WalWriterStats;
+
 /*
  * Updated by pgstat_count_buffer_*_time macros
  */
@@ -858,6 +875,7 @@ 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