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 <[email protected]>
Reviewed-by: Ashutosh Bapat <[email protected]>
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
index c036a2c37b6dc6e44e0747498b85b39bc48e980c..899acfd912fc5d5dbb9489c7359063a23214a28b 100644 (file)
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -847,6 +847,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
        ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
        TransactionId effective_xmin;
        TransactionId effective_catalog_xmin;
+       bool        invalidated;
 
        if (!s->in_use)
            continue;
@@ -854,8 +855,14 @@ 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 283517d95666c84a18197a57945d8676340270ac..06918759e7c30a139195736703b488afb665dd6d 100644 (file)
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -3901,6 +3901,9 @@ ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin,
 
    if (!already_locked)
        LWLockRelease(ProcArrayLock);
+
+   elog(DEBUG1, "xmin required by slots: data %u, catalog %u",
+        xmin, catalog_xmin);
 }
 
 /*