Re: Re: Proposal for Allow postgresql.conf values to be changed via SQL [review]

2013-02-11 15:25 keltezéssel, Andres Freund írta:
> On 2013-02-11 15:21:13 +0100, Boszormenyi Zoltan wrote:
>> 2013-01-24 18:02 keltezéssel, Tom Lane írta:
>>> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
>>>> On 2013-01-24 11:22:52 -0500, Tom Lane wrote:
>>>>> Say again? Surely the temp file is being written by whichever backend
>>>>> is executing SET PERSISTENT, and there could be more than one.
>>>> Sure, but the patch acquires SetPersistentLock exlusively beforehand
>>>> which seems fine to me.
>>> Why should we have such a lock? Seems like that will probably introduce
>>> as many problems as it fixes. Deadlock risk, blockages, etc. It is not
>>> necessary for atomicity, since rename() would be atomic already.
>> There is a problem when running SET PERSISTENT for different GUCs
>> in parallel. All happen to read the same original file, and only one
>> setting ends up in the result if you rely only on the rename() being atomic.
>> The LWLock provides the serialization for that problem.
> Tom was voting for one-setting-per-file, in that case the problem
> doesn't exist.

I voted for the one-file approach and was arguing from the POV
of the current implementation.

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Zoltán Böszörményi
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