make_wal_replay_pause_synchronous.patch

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8e3b5df7dc..26aadb4178 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -6076,6 +6076,20 @@ void
 SetRecoveryPause(bool recoveryPause)
 {
 	SpinLockAcquire(&XLogCtl->info_lck);
+
+	/*
+	 * Wait for the application of the record being applied to finish, so that
+	 * no records will be applied after this function returns. We don't need to
+	 * wait when ending a pause. Anyway we are requesting a recovery pause, we
+	 * don't mind a possible slow down of recovery by the info_lck here.
+	 */
+	while(recoveryPause && !XLogCtl->recoveryPause &&
+		  XLogCtl->replayEndRecPtr != XLogCtl->lastReplayedEndRecPtr)
+	{
+		SpinLockRelease(&XLogCtl->info_lck);
+		pg_usleep(10000L);		/* 10 ms */
+		SpinLockAcquire(&XLogCtl->info_lck);
+	}
 	XLogCtl->recoveryPause = recoveryPause;
 	SpinLockRelease(&XLogCtl->info_lck);
 }
@@ -7262,6 +7276,7 @@ StartupXLOG(void)
 			do
 			{
 				bool		switchedTLI = false;
+				bool		pause_requested = false;
 
 #ifdef WAL_DEBUG
 				if (XLOG_DEBUG ||
@@ -7292,11 +7307,9 @@ StartupXLOG(void)
 				 * Note that we intentionally don't take the info_lck spinlock
 				 * here.  We might therefore read a slightly stale value of
 				 * the recoveryPause flag, but it can't be very stale (no
-				 * worse than the last spinlock we did acquire).  Since a
-				 * pause request is a pretty asynchronous thing anyway,
-				 * possibly responding to it one WAL record later than we
-				 * otherwise would is a minor issue, so it doesn't seem worth
-				 * adding another spinlock cycle to prevent that.
+				 * worse than the last spinlock we did acquire). We eventually
+				 * make sure catching the pause request if any just before
+				 * applying this record.
 				 */
 				if (((volatile XLogCtlData *) XLogCtl)->recoveryPause)
 					recoveryPausesHere(false);
@@ -7385,12 +7398,19 @@ StartupXLOG(void)
 				/*
 				 * Update shared replayEndRecPtr before replaying this record,
 				 * so that XLogFlush will update minRecoveryPoint correctly.
+				 * Also we check for the correct value of the recoveryPause
+				 * flag here not to have redo overrun during a pause. See
+				 * SetRecoveryPuase() for details.
 				 */
 				SpinLockAcquire(&XLogCtl->info_lck);
 				XLogCtl->replayEndRecPtr = EndRecPtr;
 				XLogCtl->replayEndTLI = ThisTimeLineID;
+				pause_requested = XLogCtl->recoveryPause;
 				SpinLockRelease(&XLogCtl->info_lck);
 
+				if (pause_requested)
+					recoveryPausesHere(false);
+					
 				/*
 				 * If we are attempting to enter Hot Standby mode, process
 				 * XIDs we see