From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tomas Vondra <tv(at)fuzzy(dot)cz>, Thom Brown <thom(at)linux(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: change in LOCK behavior |
Date: | 2012-11-26 15:55:47 |
Message-ID: | 12289.1353945347@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
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?
regards, tom lane
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