From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Boszormenyi Zoltan <zb(at)cybertec(dot)at> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Amit Kapila <amit(dot)kapila(at)huawei(dot)com>, 'Robert Haas' <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Re: Proposal for Allow postgresql.conf values to be changed via SQL [review] |
Date: | 2013-02-11 14:25:17 |
Message-ID: | 20130211142517.GA30054@awork2.anarazel.de |
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Lists: | pgsql-hackers |
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.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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