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commit    295f75b4bb60c22acb7bdcd7aebf7bb8965658aa
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Wed Sep 30 05:37:19 2026 +0000

    Fix clobbering of proc entry's statusFlags during slot invalidation
    
    ReplicationSlotRelease() copied MyProc->statusFlags unconditionally
    when resetting PROC_IN_LOGICAL_DECODING, using its pgxactoff to decide
    which area to update.
    
    Slot invalidations can be done by the checkpointer or the startup
    process, and ReplicationSlotRelease() ignored the fact that pgxactoff is
    only meaningful for processes in the proc array, that auxiliary
    processes never join.  pgxactoff would remain at 0 for these, meaning
    that an incorrect set of status flags would be updated.
    
    The consequences of this issue could be various, depending on the
    statsFlags lost in the proc slot incorrectly overwritten.  Losing
    PROC_AFFECTS_ALL_HORIZONS has been mentioned as the worse case, causing
    VACUUM to remove rows a standby may needs even if standby feedback is
    enabled.  Assertions failures are another possibility.
    
    Let's skip the update of statusFlags unless PROC_IN_LOGICAL_DECODING is
    set.  Nothing but StartupDecodingContext() sets it, and no auxiliary
    processes call it.
    
    Author: Vlad Lesin <vladlesin@gmail.com>
    Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
    Reviewed-by: Michael Paquier <michael@paquier.xyz>
    Discussion: https://postgr.es/m/889a06dd-45fc-423b-9dd2-87d5b5dc60c6@gmail.com
    Backpatch-through: 14


 src/backend/replication/slot.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 2f1696f4111..1f3bb7f7f87 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -747,11 +747,19 @@ ReplicationSlotRelease(void)
 		MyReplicationSlot = NULL;
 	}
 
-	/* might not have been set when we've been a plain slot */
-	LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
-	MyProc->statusFlags &= ~PROC_IN_LOGICAL_DECODING;
-	ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
-	LWLockRelease(ProcArrayLock);
+	/*
+	 * Update statusFlags only if PROC_IN_LOGICAL_DECODING is set.  An
+	 * auxiliary process (checkpointer or startup process) may invalidate a
+	 * slot.  Auxiliary processes are not in the proc array, and pgxactoff
+	 * would point at something which is not its own.
+	 */
+	if (MyProc->statusFlags & PROC_IN_LOGICAL_DECODING)
+	{
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags &= ~PROC_IN_LOGICAL_DECODING;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+	}
 
 	if (am_walsender)
 	{


[parent: 104bec3af45c]