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commit    1ad033df16df8d9f9e9f597ca31915266dfbdfb9
Author:   Alvaro Herrera <alvherre@alvh.no-ip.org>
Date:     Tue Nov 22 09:56:07 2022 +0000
First released in: 16.0, 13.10, 14.7, 15.2

    Ignore invalidated slots while computing oldest catalog Xmin
    
    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


 src/backend/replication/slot.c      | 7 +++++++
 src/backend/storage/ipc/procarray.c | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 329599e99de..80d96db8eb9 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -846,6 +846,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
 		TransactionId effective_catalog_xmin;
+		bool		invalidated;
 
 		if (!s->in_use)
 			continue;
@@ -853,8 +854,14 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 		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
index dadaa958a84..0d197210461 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -3900,6 +3900,9 @@ ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin,
 
 	if (!already_locked)
 		LWLockRelease(ProcArrayLock);
+
+	elog(DEBUG1, "xmin required by slots: data %u, catalog %u",
+		 xmin, catalog_xmin);
 }
 
 /*


[parent: 4f997ad06255]