Re: change in LOCK behavior

On Mon, Nov 26, 2012 at 10:55 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>> On 11 October 2012 20:43, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>>> So we have to take the snapshot before you begin execution, but it
>>>> seems that to avoid surprising behavior we also have to take it after
>>>> acquiring locks. And it looks like locking is intertwined with a
>>>> bunch of other parse analysis tasks that might require a snapshot to
>>>> have been taken first. Whee.
>
>>> Yeah. I think that a good solution to this would involve guaranteeing
>>> that the execution snapshot is not taken until we have all locks that
>>> are going to be taken on the tables. Which is likely to involve a fair
>>> amount of refactoring, though I admit I've not looked at details.
>>>
>>> In any case, it's a mistake to think about this in isolation. If we're
>>> going to do something about redefining SnapshotNow to avoid its race
>>> conditions, that's going to move the goalposts quite a lot.
>>>
>>> Anyway, my feeling about it is that I don't want 9.2 to have an
>>> intermediate behavior between the historical one and whatever we end up
>>> designing to satisfy these concerns. That's why I'm pressing for
>>> reversion and not a band-aid fix in 9.2. I certainly hope we can do
>>> better going forward, but this is not looking like whatever we come up
>>> with would be sane to back-patch.
>
>> Agreed, please revert.
>
> We have to do something about this one way or another before we can ship
> 9.2.2. Is the consensus to revert this patch:
> http://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=d573e239f03506920938bf0be56c868d9c3416da
> and if so, who's going to do the deed?

I was assuming you were going to do it.

--
Robert Haas
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