Alvaro Herrera <[EMAIL PROTECTED]> writes:
> I was thinking at what time was the most appropiate to insert or remove
> an Xid from the cache.  We can do without any excl-locking because 1) we
> already assume the storing of an Xid to be atomic, and 2) no one can be
> interested in querying for an Xid before the originating transaction has
> had the chance to write a tuple with that Xid anyway.

Actually ... that fails if GetSnapshotData is going to copy subtrans
XIDs.  So this area needs more thought.

> On the third hand, are we going to sh-acquire the ProcArray lock while a
> GetSnapshotData copies all subxact Xids of all running transactions?
> ProcArrayLock will become more of a contention point than it already is.

Yeah, but sharelock is better than exclusive lock ...

                        regards, tom lane

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