"Pavan Deolasee" <[EMAIL PROTECTED]> 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 relcache entry before we try to use it.
     * We can skip this in the not-uncommon case that we already had the same
     * type of lock being requested, since then no one else could have
     * modified the relcache entry in an undesirable way.  (In the case where
     * our own xact modifies the rel, the relcache update happens via
     * CommandCounterIncrement, not here.)

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

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