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Fix clobbering of proc entry's statusFlags during slot invalidation

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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
This commit is contained in:
Michael Paquier
2026-09-30 14:37:19 +09:00
parent 104bec3af4
commit 295f75b4bb
1 changed files with 13 additions and 5 deletions
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18
src/backend/replication/slot.c
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@@ -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)
{