v18-0005-send-stats-for-bgwriter-when-shutdown.patch

diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 715d5195bb..7cd01b38e9 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -83,6 +83,8 @@ int			BgWriterDelay = 200;
 static TimestampTz last_snapshot_ts;
 static XLogRecPtr last_snapshot_lsn = InvalidXLogRecPtr;
 
+/* Prototypes for private functions */
+static void HandleBackgroundWriterInterrupts(void);
 
 /*
  * Main entry point for bgwriter process
@@ -236,7 +238,7 @@ BackgroundWriterMain(void)
 		/* Clear any already-pending wakeups */
 		ResetLatch(MyLatch);
 
-		HandleMainLoopInterrupts();
+		HandleBackgroundWriterInterrupts();
 
 		/*
 		 * Do one cycle of dirty-buffer writing.
@@ -244,9 +246,11 @@ BackgroundWriterMain(void)
 		can_hibernate = BgBufferSync(&wb_context);
 
 		/*
-		 * Send off activity statistics to the stats collector
+		 * Send off activity statistics to the stats collector. Since
+		 * LogStandbySnapshot() will generate the WAL, send the WAL stats too.
 		 */
-		pgstat_send_bgwriter();
+		pgstat_send_bgwriter(false);
+		pgstat_send_wal(false);
 
 		if (FirstCallSinceLastCheckpoint())
 		{
@@ -349,3 +353,36 @@ BackgroundWriterMain(void)
 		prev_hibernate = can_hibernate;
 	}
 }
+
+/*
+ * Interrupt handler for main loops of Background Writer process.
+ */
+static void
+HandleBackgroundWriterInterrupts(void)
+{
+	if (ProcSignalBarrierPending)
+		ProcessProcSignalBarrier();
+
+	if (ConfigReloadPending)
+	{
+		ConfigReloadPending = false;
+		ProcessConfigFile(PGC_SIGHUP);
+	}
+
+	if (ShutdownRequestPending)
+	{
+		/*
+		 * Force to send remaining statistics to the stats collector at
+		 * process exit.
+		 *
+		 * Since pgstat_send_bgwriter and pgstat_send_wal are invoked with
+		 * 'force' is false in main loop to avoid overloading to the stats
+		 * collector, there may exist unsent stats counters for the background
+		 * writer.
+		 */
+		pgstat_send_bgwriter(true);
+		pgstat_send_wal(true);
+
+		proc_exit(0);
+	}
+}
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 94b55a17b3..c5f197434c 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -502,10 +502,10 @@ CheckpointerMain(void)
 		 * worth the trouble to split the stats support into two independent
 		 * stats message types.)
 		 */
-		pgstat_send_bgwriter();
+		pgstat_send_bgwriter(true);
 
 		/* Send WAL statistics to the stats collector. */
-		pgstat_report_wal();
+		pgstat_send_wal(true);
 
 		/*
 		 * If any checkpoint flags have been set, redo the loop to handle the
@@ -582,8 +582,8 @@ HandleCheckpointerInterrupts(void)
 		 */
 		BgWriterStats.m_requested_checkpoints++;
 		ShutdownXLOG(0, 0);
-		pgstat_send_bgwriter();
-		pgstat_report_wal();
+		pgstat_send_bgwriter(true);
+		pgstat_send_wal(true);
 
 		/* Normal exit from the checkpointer is here */
 		proc_exit(0);			/* done */
@@ -724,7 +724,7 @@ CheckpointWriteDelay(int flags, double progress)
 		/*
 		 * Report interim activity statistics to the stats collector.
 		 */
-		pgstat_send_bgwriter();
+		pgstat_send_bgwriter(true);
 
 		/*
 		 * This sleep used to be connected to bgwriter_delay, typically 200ms.
diff --git a/src/backend/postmaster/interrupt.c b/src/backend/postmaster/interrupt.c
index dd9136a942..6522cb311f 100644
--- a/src/backend/postmaster/interrupt.c
+++ b/src/backend/postmaster/interrupt.c
@@ -26,31 +26,12 @@
 volatile sig_atomic_t ConfigReloadPending = false;
 volatile sig_atomic_t ShutdownRequestPending = false;
 
-/*
- * Simple interrupt handler for main loops of background processes.
- */
-void
-HandleMainLoopInterrupts(void)
-{
-	if (ProcSignalBarrierPending)
-		ProcessProcSignalBarrier();
-
-	if (ConfigReloadPending)
-	{
-		ConfigReloadPending = false;
-		ProcessConfigFile(PGC_SIGHUP);
-	}
-
-	if (ShutdownRequestPending)
-		proc_exit(0);
-}
-
 /*
  * Simple signal handler for triggering a configuration reload.
  *
  * Normally, this handler would be used for SIGHUP. The idea is that code
  * which uses it would arrange to check the ConfigReloadPending flag at
- * convenient places inside main loops, or else call HandleMainLoopInterrupts.
+ * convenient places inside main loops.
  */
 void
 SignalHandlerForConfigReload(SIGNAL_ARGS)
@@ -98,7 +79,7 @@ SignalHandlerForCrashExit(SIGNAL_ARGS)
  * or SIGTERM.
  *
  * ShutdownRequestPending should be checked at a convenient place within the
- * main loop, or else the main loop should call HandleMainLoopInterrupts.
+ * main loop.
  */
 void
 SignalHandlerForShutdownRequest(SIGNAL_ARGS)
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index b1e2d94951..de16696dc6 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -146,8 +146,8 @@ PgStat_MsgWal WalStats;
 
 /*
  * WAL usage counters saved from pgWALUsage at the previous call to
- * pgstat_report_wal(). This is used to calculate how much WAL usage
- * happens between pgstat_report_wal() calls, by substracting
+ * pgstat_send_wal(). This is used to calculate how much WAL usage
+ * happens between pgstat_send_wal() calls, by substracting
  * the previous counters from the current ones.
  */
 static WalUsage prevWalUsage;
@@ -975,7 +975,7 @@ pgstat_report_stat(bool disconnect)
 	pgstat_send_funcstats();
 
 	/* Send WAL statistics */
-	pgstat_report_wal();
+	pgstat_send_wal(true);
 
 	/* Finally send SLRU statistics */
 	pgstat_send_slru();
@@ -3118,7 +3118,7 @@ pgstat_initialize(void)
 	}
 
 	/*
-	 * Initialize prevWalUsage with pgWalUsage so that pgstat_report_wal() can
+	 * Initialize prevWalUsage with pgWalUsage so that pgstat_send_wal() can
 	 * calculate how much pgWalUsage counters are increased by substracting
 	 * prevWalUsage from pgWalUsage.
 	 */
@@ -4643,13 +4643,19 @@ pgstat_send_archiver(const char *xlog, bool failed)
  * pgstat_send_bgwriter() -
  *
  *		Send bgwriter statistics to the collector
+ *
+ * If 'force' is not set, bgwriter stats message is only sent if enough time has
+ * passed since last one was sent to reach PGSTAT_STAT_INTERVAL.
+ *
+ * Return true if the message is sent, and false otherwise.
  * ----------
  */
 void
-pgstat_send_bgwriter(void)
+pgstat_send_bgwriter(bool force)
 {
 	/* We assume this initializes to zeroes */
 	static const PgStat_MsgBgWriter all_zeroes;
+	static TimestampTz sendTime = 0;
 
 	/*
 	 * This function can be called even if nothing at all has happened. In
@@ -4659,6 +4665,19 @@ pgstat_send_bgwriter(void)
 	if (memcmp(&BgWriterStats, &all_zeroes, sizeof(PgStat_MsgBgWriter)) == 0)
 		return;
 
+	if (!force)
+	{
+		TimestampTz now = GetCurrentTimestamp();
+
+		/*
+		 * Don't send a message unless it's been at least PGSTAT_STAT_INTERVAL
+		 * msec since we last sent one.
+		 */
+		if (!TimestampDifferenceExceeds(sendTime, now, PGSTAT_STAT_INTERVAL))
+			return;
+		sendTime = now;
+	}
+
 	/*
 	 * Prepare and send the message
 	 */
@@ -4672,19 +4691,25 @@ pgstat_send_bgwriter(void)
 }
 
 /* ----------
- * pgstat_report_wal() -
+ * pgstat_send_wal() -
  *
- * Calculate how much WAL usage counters are increased and send
- * WAL statistics to the collector.
+ *	Send WAL statistics to the collector.
  *
- * Must be called by processes that generate WAL.
+ * If 'force' is not set, WAL stats message is only sent if enough time has
+ * passed since last one was sent to reach PGSTAT_STAT_INTERVAL.
+ *
+ * Return true if the message is sent, and false otherwise.
  * ----------
  */
 void
-pgstat_report_wal(void)
+pgstat_send_wal(bool force)
 {
 	WalUsage	walusage;
 
+	/* We assume this initializes to zeroes */
+	static const PgStat_MsgWal all_zeroes;
+	static TimestampTz sendTime = 0;
+
 	/*
 	 * Calculate how much WAL usage counters are increased by substracting the
 	 * previous counters from the current ones. Fill the results in WAL stats
@@ -4697,43 +4722,13 @@ pgstat_report_wal(void)
 	WalStats.m_wal_fpi = walusage.wal_fpi;
 	WalStats.m_wal_bytes = walusage.wal_bytes;
 
-	/*
-	 * Send WAL stats message to the collector.
-	 */
-	if (!pgstat_send_wal(true))
-		return;
-
-	/*
-	 * Save the current counters for the subsequent calculation of WAL usage.
-	 */
-	prevWalUsage = pgWalUsage;
-}
-
-/* ----------
- * pgstat_send_wal() -
- *
- *	Send WAL statistics to the collector.
- *
- * If 'force' is not set, WAL stats message is only sent if enough time has
- * passed since last one was sent to reach PGSTAT_STAT_INTERVAL.
- *
- * Return true if the message is sent, and false otherwise.
- * ----------
- */
-bool
-pgstat_send_wal(bool force)
-{
-	/* We assume this initializes to zeroes */
-	static const PgStat_MsgWal all_zeroes;
-	static TimestampTz sendTime = 0;
-
 	/*
 	 * 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(&WalStats, &all_zeroes, sizeof(PgStat_MsgWal)) == 0)
-		return false;
+		return;
 
 	if (!force)
 	{
@@ -4744,7 +4739,7 @@ pgstat_send_wal(bool force)
 		 * msec since we last sent one.
 		 */
 		if (!TimestampDifferenceExceeds(sendTime, now, PGSTAT_STAT_INTERVAL))
-			return false;
+			return;
 		sendTime = now;
 	}
 
@@ -4759,7 +4754,10 @@ pgstat_send_wal(bool force)
 	 */
 	MemSet(&WalStats, 0, sizeof(WalStats));
 
-	return true;
+	/*
+	 * Save the current counters for the subsequent calculation of WAL usage.
+	 */
+	prevWalUsage = pgWalUsage;
 }
 
 /* ----------
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index be43c04802..993b774bb9 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -1600,9 +1600,8 @@ extern void pgstat_twophase_postabort(TransactionId xid, uint16 info,
 									  void *recdata, uint32 len);
 
 extern void pgstat_send_archiver(const char *xlog, bool failed);
-extern void pgstat_send_bgwriter(void);
-extern void pgstat_report_wal(void);
-extern bool pgstat_send_wal(bool force);
+extern void pgstat_send_bgwriter(bool force);
+extern void pgstat_send_wal(bool force);
 
 /* ----------
  * Support functions for the SQL-callable functions to
diff --git a/src/include/postmaster/interrupt.h b/src/include/postmaster/interrupt.h
index 85a1293ef1..0d333b819a 100644
--- a/src/include/postmaster/interrupt.h
+++ b/src/include/postmaster/interrupt.h
@@ -24,7 +24,6 @@
 extern PGDLLIMPORT volatile sig_atomic_t ConfigReloadPending;
 extern PGDLLIMPORT volatile sig_atomic_t ShutdownRequestPending;
 
-extern void HandleMainLoopInterrupts(void);
 extern void SignalHandlerForConfigReload(SIGNAL_ARGS);
 extern void SignalHandlerForCrashExit(SIGNAL_ARGS);
 extern void SignalHandlerForShutdownRequest(SIGNAL_ARGS);