Re: Snapshot management, final

Alvaro Herrera <alvherre@commandprompt.com> writes:
> Tom Lane wrote:
>> Hmm ... but that "close" can't unregister the snapshot immediately,
>> because you'd lose if the 2nd savepoint gets rolled back, no?  Is the
>> handling of this case even correct at the moment?

> No, CLOSE is not rolled back:
> ...
> Maybe this is possible to fix, but again I think it's outside the scope
> of this patch.

I'd forgotten that ... seems a bit bogus, and it's certainly not
documented on the CLOSE reference page.

>> ISTM correct handling of this example would require that the "close"
>> not really discard the snap until commit.  Then, given proper ordering
>> of the cleanup operations at commit, you might be able to still have the
>> cross-check about s_level in UnregisterSnapshot.  (IOW, maybe having
>> snapshot cleanup be late in the commit sequence wasn't such a good
>> choice...)

> Right -- I'll move them earlier.

Well, without a clear idea of where to place them instead, you might as
well leave it alone for the moment.  I'd like to see this revisited
sometime though.

            regards, tom lane