v8-0003-Remove-redundant-WAIT-FOR-LSN-caller-side-pre-che.patch

From ee45997619df3712e87346146e8ae98df585a8c2 Mon Sep 17 00:00:00 2001
From: alterego655 <824662526@qq.com>
Date: Fri, 10 Apr 2026 11:05:46 +0800
Subject: [PATCH v8 3/7] Remove redundant WAIT FOR LSN caller-side pre-checks

All five wakeup call sites duplicate WaitLSNWakeup()'s internal
fast-path minWaitedLSN check and add an unnecessary NULL check
on waitLSNState.

Remove the inline pre-checks and call WaitLSNWakeup() directly.
The fast-path check inside WaitLSNWakeup() already returns early
when no waiter's target has been reached, so there is no
performance difference.

The waitLSNState NULL checks are also unnecessary: shared memory
is fully initialized before any backend or auxiliary process
starts, so waitLSNState is always non-NULL at these call sites.

Reported-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/jzq5shdewncpxc35r3s2mcfsmo4bjovkza5mnqf5bdfumhfi3g%40bglckf7dxmw5
Author: Xuneng Zhou <xunengzhou@gmail.com>
---
 src/backend/access/transam/xlog.c         | 16 ++++++----------
 src/backend/access/transam/xlogrecovery.c | 11 ++++-------
 src/backend/replication/walreceiver.c     | 17 ++++++-----------
 3 files changed, 16 insertions(+), 28 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f85b5286086..b5801ab663e 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2936,12 +2936,10 @@ XLogFlush(XLogRecPtr record)
 	WalSndWakeupProcessRequests(true, !RecoveryInProgress());
 
 	/*
-	 * If we flushed an LSN that someone was waiting for, notify the waiters.
+	 * Wake up processes waiting for primary flush LSN to reach current flush
+	 * position.
 	 */
-	if (waitLSNState &&
-		(LogwrtResult.Flush >=
-		 pg_atomic_read_u64(&waitLSNState->minWaitedLSN[WAIT_LSN_TYPE_PRIMARY_FLUSH])))
-		WaitLSNWakeup(WAIT_LSN_TYPE_PRIMARY_FLUSH, LogwrtResult.Flush);
+	WaitLSNWakeup(WAIT_LSN_TYPE_PRIMARY_FLUSH, LogwrtResult.Flush);
 
 	/*
 	 * If we still haven't flushed to the request point then we have a
@@ -3126,12 +3124,10 @@ XLogBackgroundFlush(void)
 	WalSndWakeupProcessRequests(true, !RecoveryInProgress());
 
 	/*
-	 * If we flushed an LSN that someone was waiting for, notify the waiters.
+	 * Wake up processes waiting for primary flush LSN to reach current flush
+	 * position.
 	 */
-	if (waitLSNState &&
-		(LogwrtResult.Flush >=
-		 pg_atomic_read_u64(&waitLSNState->minWaitedLSN[WAIT_LSN_TYPE_PRIMARY_FLUSH])))
-		WaitLSNWakeup(WAIT_LSN_TYPE_PRIMARY_FLUSH, LogwrtResult.Flush);
+	WaitLSNWakeup(WAIT_LSN_TYPE_PRIMARY_FLUSH, LogwrtResult.Flush);
 
 	/*
 	 * Great, done. To take some work off the critical path, try to initialize
diff --git a/src/backend/access/transam/xlogrecovery.c b/src/backend/access/transam/xlogrecovery.c
index c236e2b7969..4f2eaa36990 100644
--- a/src/backend/access/transam/xlogrecovery.c
+++ b/src/backend/access/transam/xlogrecovery.c
@@ -1782,14 +1782,11 @@ PerformWalRecovery(void)
 			ApplyWalRecord(xlogreader, record, &replayTLI);
 
 			/*
-			 * If we replayed an LSN that someone was waiting for then walk
-			 * over the shared memory array and set latches to notify the
-			 * waiters.
+			 * Wake up processes waiting for standby replay LSN to reach
+			 * current replay position.
 			 */
-			if (waitLSNState &&
-				(XLogRecoveryCtl->lastReplayedEndRecPtr >=
-				 pg_atomic_read_u64(&waitLSNState->minWaitedLSN[WAIT_LSN_TYPE_STANDBY_REPLAY])))
-				WaitLSNWakeup(WAIT_LSN_TYPE_STANDBY_REPLAY, XLogRecoveryCtl->lastReplayedEndRecPtr);
+			WaitLSNWakeup(WAIT_LSN_TYPE_STANDBY_REPLAY,
+						  XLogRecoveryCtl->lastReplayedEndRecPtr);
 
 			/* Exit loop if we reached inclusive recovery target */
 			if (recoveryStopsAfter(xlogreader))
diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c
index c0ac75b54d7..8ed796f3033 100644
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -978,12 +978,10 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr, TimeLineID tli)
 	pg_atomic_write_membarrier_u64(&WalRcv->writtenUpto, LogstreamResult.Write);
 
 	/*
-	 * If we wrote an LSN that someone was waiting for, notify the waiters.
+	 * Wake up processes waiting for standby write LSN to reach current write
+	 * position.
 	 */
-	if (waitLSNState &&
-		(LogstreamResult.Write >=
-		 pg_atomic_read_u64(&waitLSNState->minWaitedLSN[WAIT_LSN_TYPE_STANDBY_WRITE])))
-		WaitLSNWakeup(WAIT_LSN_TYPE_STANDBY_WRITE, LogstreamResult.Write);
+	WaitLSNWakeup(WAIT_LSN_TYPE_STANDBY_WRITE, LogstreamResult.Write);
 
 	/*
 	 * Close the current segment if it's fully written up in the last cycle of
@@ -1025,13 +1023,10 @@ XLogWalRcvFlush(bool dying, TimeLineID tli)
 		SpinLockRelease(&walrcv->mutex);
 
 		/*
-		 * If we flushed an LSN that someone was waiting for, notify the
-		 * waiters.
+		 * Wake up processes waiting for standby flush LSN to reach current
+		 * flush position.
 		 */
-		if (waitLSNState &&
-			(LogstreamResult.Flush >=
-			 pg_atomic_read_u64(&waitLSNState->minWaitedLSN[WAIT_LSN_TYPE_STANDBY_FLUSH])))
-			WaitLSNWakeup(WAIT_LSN_TYPE_STANDBY_FLUSH, LogstreamResult.Flush);
+		WaitLSNWakeup(WAIT_LSN_TYPE_STANDBY_FLUSH, LogstreamResult.Flush);
 
 		/* Signal the startup process and walsender that new WAL has arrived */
 		WakeupRecovery();
-- 
2.51.0