Re: Standby server with cascade logical replication could not be properly stopped under load

On Thu, May 22, 2025 at 09:22:02PM +0300, Alexey Makhmutov wrote:
> I've tried to update method comment as well in the updated patch:
> 0001-Use-only-replayed-position-as-target-flush-point-3-pg-master.patch.
> The same patch could be applied on top of PG 17 as well.

+	if (MyWalSnd->kind == REPLICATION_KIND_PHYSICAL)
+	{
+		TimeLineID	receiveTLI;
+		XLogRecPtr	receivePtr = GetWalRcvFlushRecPtr(NULL, &receiveTLI);
+
+		if (receiveTLI == replayTLI && receivePtr > result)
+			result = receivePtr;
+	}

Looking at the patch, I am not much a fan of looking at MyWalSnd in
GetStandbyFlushRecPtr() which does not have such a dependency yet, to
then decide if the LSN retrieved by GetWalRcvFlushRecPtr() should be
removed or used.

Wouldn't it be better to extend GetStandbyFlushRecPtr() so as the
caller can directly decide if they want to include in the maths the
last LSN flushed by the WAL receiver, depending on the code path where
the routine is called?  That makes for a larger patch, of course, but
it removes the need to look at MyWalSnd inside
GetStandbyFlushRecPtr().
--
Michael