Ignore invalidated slots while computing oldest catalog Xmin

alvherre · alvherre · commit 1b3ed757145d · 2022-11-22T10:56:07.000+01:00
Once a logical slot has acquired a catalog_xmin, it doesn't let go of it, even when invalidated by exceeding the max_slot_wal_keep_size, which means that dead catalog tuples are not removed by vacuum anymore since the point is invalidated, until the slot is dropped. This could be catastrophic if catalog churn is high. Change the computation of Xmin to ignore invalidated slots, to prevent dead rows from accumulating. Backpatch to 13, where slot invalidation appeared. Author: Sirisha Chamarthi <sirichamarthi22@gmail.com> Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> Discussion: https://postgr.es/m/CAKrAKeUEDeqquN9vwzNeG-CN8wuVsfRYbeOUV9qKO_RHok=j+g@mail.gmail.com
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
@@ -778,15 +778,22 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
 		TransactionId effective_catalog_xmin;
+		bool		invalidated;
 
 		if (!s->in_use)
 			continue;
 
 		SpinLockAcquire(&s->mutex);
 		effective_xmin = s->effective_xmin;
 		effective_catalog_xmin = s->effective_catalog_xmin;
+		invalidated = (!XLogRecPtrIsInvalid(s->data.invalidated_at) &&
+					   XLogRecPtrIsInvalid(s->data.restart_lsn));
 		SpinLockRelease(&s->mutex);
 
+		/* invalidated slots need not apply */
+		if (invalidated)
+			continue;
+
 		/* check the data xmin */
 		if (TransactionIdIsValid(effective_xmin) &&
 			(!TransactionIdIsValid(agg_xmin) ||
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
@@ -3946,6 +3946,9 @@ ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin,
 
 	if (!already_locked)
 		LWLockRelease(ProcArrayLock);
+
+	elog(DEBUG1, "xmin required by slots: data %u, catalog %u",
+		 xmin, catalog_xmin);
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -3946,6 +3946,9 @@ ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin,`
`3946`	`3946`
`3947`	`3947`	`if (!already_locked)`
`3948`	`3948`	`LWLockRelease(ProcArrayLock);`
	`3949`	`+`
	`3950`	`+ elog(DEBUG1, "xmin required by slots: data %u, catalog %u",`
	`3951`	`+ xmin, catalog_xmin);`
`3949`	`3952`	`}`
`3950`	`3953`
`3951`	`3954`	`/*`