Re: POC: enable logical decoding when wal_level = 'replica' without a server restart

Hi Sawada-San.

Some review comments for v24-0001.

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src/backend/replication/slot.c

ReplicationSlotsDropDBSlots:

1.
  LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
  for (i = 0; i < max_replication_slots; i++)
  {
  ReplicationSlot *s;
+ bool invalidated;
  char    *slotname;
  int active_pid;

@@ -1462,11 +1494,22 @@ restart:
  if (!SlotIsLogical(s))
  continue;

+ SpinLockAcquire(&s->mutex);
+ invalidated = s->data.invalidated == RS_INVAL_NONE;
+ SpinLockRelease(&s->mutex);
+
+ /*
+ * Count slots on other databases too so we can disable logical
+ * decoding only if no slots in the cluster.
+ */
+ if (invalidated)
+ n_valid_logicalslots++;
+

IMO it's misleading/backwards to have bool invalidated == true when
the invalidated member is RS_INVAL_NONE.

It's fine to rename the bool var as 'invalidated', but don't you also
need to reverse the assignment to (s->data.invalidated !=
RS_INVAL_NONE) instead of (s->data.invalidated == RS_INVAL_NONE)?

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Kind Regards,
Peter Smith.
Fujitsu Australia