Run checkpointer and bgwriter in crash recovery.

Start up the checkpointer and bgwriter during crash recovery (except in
--single mode), as we do for replication.  This wasn't done back in
commit cdd46c76 out of caution.  Now it seems like a better idea to make
the environment as similar as possible in both cases.  There may also be
some performance advantages.

Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Tested-by: Jakub Wartak <Jakub.Wartak@tomtom.com>
Discussion: https://postgr.es/m/CA%2BhUKGJ8NRsqgkZEnsnRc2MFROBV-jCnacbYvtpptK2A9YYp9Q%40mail.gmail.com

src/backend/access/transam/xlog.c

@@ -869,9 +869,6 @@ bool		reachedConsistency = false;
 
 static bool InRedo = false;
 
-/* Have we launched bgwriter during recovery? */
-static bool bgwriterLaunched = false;
-
 /* For WALInsertLockAcquire/Release functions */
 static int	MyLockNo = 0;
 static bool holdingAllLocks = false;
@@ -7311,25 +7308,15 @@ StartupXLOG(void)
 		/* Also ensure XLogReceiptTime has a sane value */
 		XLogReceiptTime = GetCurrentTimestamp();
 
+		/* Allow ProcSendSignal() to find us, for buffer pin wakeups. */
+		PublishStartupProcessInformation();
+
 		/*
 		 * Let postmaster know we've started redo now, so that it can launch
-		 * checkpointer to perform restartpoints.  We don't bother during
-		 * crash recovery as restartpoints can only be performed during
-		 * archive recovery.  And we'd like to keep crash recovery simple, to
-		 * avoid introducing bugs that could affect you when recovering after
-		 * crash.
-		 *
-		 * After this point, we can no longer assume that we're the only
-		 * process in addition to postmaster!  Also, fsync requests are
-		 * subsequently to be handled by the checkpointer, not locally.
+		 * the archiver if necessary.
 		 */
-		if (ArchiveRecoveryRequested && IsUnderPostmaster)
-		{
-			PublishStartupProcessInformation();
-			EnableSyncRequestForwarding();
+		if (IsUnderPostmaster)
 			SendPostmasterSignal(PMSIGNAL_RECOVERY_STARTED);
-			bgwriterLaunched = true;
-		}
 
 		/*
 		 * Allow read-only connections immediately if we're consistent
@@ -7903,7 +7890,7 @@ StartupXLOG(void)
 		 * after we're fully out of recovery mode and already accepting
 		 * queries.
 		 */
-		if (bgwriterLaunched)
+		if (ArchiveRecoveryRequested && IsUnderPostmaster)
 		{
 			if (LocalPromoteIsTriggered)
 			{
@@ -7927,7 +7914,11 @@ StartupXLOG(void)
 								  CHECKPOINT_WAIT);
 		}
 		else
-			CreateCheckPoint(CHECKPOINT_END_OF_RECOVERY | CHECKPOINT_IMMEDIATE);
+		{
+			RequestCheckpoint(CHECKPOINT_END_OF_RECOVERY |
+							  CHECKPOINT_IMMEDIATE |
+							  CHECKPOINT_WAIT);
+		}
 	}
 
 	if (ArchiveRecoveryRequested)
@@ -12182,7 +12173,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 		 * Request a restartpoint if we've replayed too much xlog since the
 		 * last one.
 		 */
-		if (bgwriterLaunched)
+		if (ArchiveRecoveryRequested && IsUnderPostmaster)
 		{
 			if (XLogCheckpointNeeded(readSegNo))
 			{

src/backend/postmaster/bgwriter.c

@@ -12,9 +12,6 @@
  *
  * As of Postgres 9.2 the bgwriter no longer handles checkpoints.
  *
- * The bgwriter is started by the postmaster as soon as the startup subprocess
- * finishes, or as soon as recovery begins if we are doing archive recovery.
- * It remains alive until the postmaster commands it to terminate.
  * Normal termination is by SIGTERM, which instructs the bgwriter to exit(0).
  * Emergency termination is by SIGQUIT; like any backend, the bgwriter will
  * simply abort and exit on SIGQUIT.

src/backend/postmaster/checkpointer.c

@@ -10,9 +10,6 @@
  * fill WAL segments; the checkpointer itself doesn't watch for the
  * condition.)
  *
- * The checkpointer is started by the postmaster as soon as the startup
- * subprocess finishes, or as soon as recovery begins if we are doing archive
- * recovery.  It remains alive until the postmaster commands it to terminate.
  * Normal termination is by SIGUSR2, which instructs the checkpointer to
  * execute a shutdown checkpoint and then exit(0).  (All backends must be
  * stopped before SIGUSR2 is issued!)  Emergency termination is by SIGQUIT;

src/backend/postmaster/postmaster.c

@@ -1403,6 +1403,12 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STARTING);
 
+	/* Start bgwriter and checkpointer so they can help with recovery */
+	if (CheckpointerPID == 0)
+		CheckpointerPID = StartCheckpointer();
+	if (BgWriterPID == 0)
+		BgWriterPID = StartBackgroundWriter();
+
 	/*
 	 * We're ready to rock and roll...
 	 */
@@ -1765,7 +1771,7 @@ ServerLoop(void)
 		 * fails, we'll just try again later.  Likewise for the checkpointer.
 		 */
 		if (pmState == PM_RUN || pmState == PM_RECOVERY ||
-			pmState == PM_HOT_STANDBY)
+			pmState == PM_HOT_STANDBY || pmState == PM_STARTUP)
 		{
 			if (CheckpointerPID == 0)
 				CheckpointerPID = StartCheckpointer();
@@ -5161,15 +5167,6 @@ sigusr1_handler(SIGNAL_ARGS)
 		FatalError = false;
 		AbortStartTime = 0;
 
-		/*
-		 * Crank up the background tasks.  It doesn't matter if this fails,
-		 * we'll just try again later.
-		 */
-		Assert(CheckpointerPID == 0);
-		CheckpointerPID = StartCheckpointer();
-		Assert(BgWriterPID == 0);
-		BgWriterPID = StartBackgroundWriter();
-
 		/*
 		 * Start the archiver if we're responsible for (re-)archiving received
 		 * files.

src/backend/storage/sync/sync.c

@@ -129,10 +129,10 @@ InitSync(void)
 {
 	/*
 	 * Create pending-operations hashtable if we need it.  Currently, we need
-	 * it if we are standalone (not under a postmaster) or if we are a startup
-	 * or checkpointer auxiliary process.
+	 * it if we are standalone (not under a postmaster) or if we are a
+	 * checkpointer auxiliary process.
 	 */
-	if (!IsUnderPostmaster || AmStartupProcess() || AmCheckpointerProcess())
+	if (!IsUnderPostmaster || AmCheckpointerProcess())
 	{
 		HASHCTL		hash_ctl;
 
@@ -589,27 +589,3 @@ RegisterSyncRequest(const FileTag *ftag, SyncRequestType type,
 
 	return ret;
 }
-
-/*
- * In archive recovery, we rely on checkpointer to do fsyncs, but we will have
- * already created the pendingOps during initialization of the startup
- * process.  Calling this function drops the local pendingOps so that
- * subsequent requests will be forwarded to checkpointer.
- */
-void
-EnableSyncRequestForwarding(void)
-{
-	/* Perform any pending fsyncs we may have queued up, then drop table */
-	if (pendingOps)
-	{
-		ProcessSyncRequests();
-		hash_destroy(pendingOps);
-	}
-	pendingOps = NULL;
-
-	/*
-	 * We should not have any pending unlink requests, since mdunlink doesn't
-	 * queue unlink requests when isRedo.
-	 */
-	Assert(pendingUnlinks == NIL);
-}

src/include/storage/sync.h

@@ -60,7 +60,6 @@ extern void SyncPreCheckpoint(void);
 extern void SyncPostCheckpoint(void);
 extern void ProcessSyncRequests(void);
 extern void RememberSyncRequest(const FileTag *ftag, SyncRequestType type);
-extern void EnableSyncRequestForwarding(void);
 extern bool RegisterSyncRequest(const FileTag *ftag, SyncRequestType type,
 								bool retryOnError);