Re: Update with subselect sometimes returns wrong result

From: Marko Tiikkaja <marko(at)joh(dot)to>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Oliver Seemann <oseemann(at)gmail(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: Update with subselect sometimes returns wrong result
Date: 2013-11-30 20:42:47
Message-ID: 529A4DC7.6000005@joh.to
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On 11/30/13, 6:57 PM, Tom Lane wrote:
> Oliver Seemann <oseemann(at)gmail(dot)com> writes:
>> And it does so, most of of the time. But when run repeatedly in a loop like
>> in the attached script, then it will occasionally return 2 rows with two
>> different id values, something the LIMIT 1 should prevent. In my tests it
>> took from anywhere between 0 to 10 minutes and on average 1 to 2 minutes to
>> trigger the problem.
>
> I failed to reproduce the claimed misbehavior in git tip of any active
> branch. I'd like to think this means we fixed the problem in the last
> two months, but I don't see anything that looks like a promising candidate
> in the commit logs. Perhaps there is some important contributing factor
> you've not mentioned --- nondefault postgresql.conf settings, for
> instance.

I've managed to reproduce this against REL9_1_STABLE
(4bdccd8427718f9c468e5e03286252f37ea771b5). I'm on OS X mavericks,
configure line: ./configure --enable-debug --with-openssl --with-perl
--with-libxml --with-readline. Compiler Apple LLVM version 5.0
(clang-500.2.79) (based on LLVM 3.3svn). No changes to postgresql.conf.

Does that help? Do you need some more information?

Regards,
Marko Tiikkaja

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