"Pavan Deolasee" <pavan.deolasee@enterprisedb.com> writes:
> I traced it a bit and it seems that the invalidation messages
> are not accepted in session 2 because the locks are already held
> on the relation.
Right, because of this coding in LockRelationOid():
/* * Now that we have the lock, check for invalidation messages, so that we * will update or flush any stale
relcacheentry before we try to use it. * We can skip this in the not-uncommon case that we already had the same *
typeof lock being requested, since then no one else could have * modified the relcache entry in an undesirable way.
(Inthe case where * our own xact modifies the rel, the relcache update happens via * CommandCounterIncrement, not
here.) */ if (res != LOCKACQUIRE_ALREADY_HELD) AcceptInvalidationMessages();
We could remove the optimization and do AcceptInvalidationMessages
always, but I think that cure would be a great deal worse than the
disease --- it would hugely increase the contention for SInvalLock.
I'm not particularly worried about missing a potential improvement
in the plan during the first command after a change is committed.
If the invalidation were something that *had* to be accounted for,
such as a dropped index, then there should be adequate locking for it;
plancache is not introducing any new bug that wasn't there before.
regards, tom lane
