From: | Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Going for "all green" buildfarm results |
Date: | 2006-08-17 08:59:24 |
Message-ID: | 44E42FEC.4040403@kaltenbrunner.cc |
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Lists: | pgsql-hackers |
Tom Lane wrote:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
>> Maybe we could write a suitable test case using Martijn's concurrent
>> testing framework.
>
> The trick is to get process A to commit between the times that process B
> looks at the new and old versions of the pg_class row (and it has to
> happen to do so in that order ... although that's not a bad bet given
> the way btree handles equal keys).
>
> I think the reason we've not tracked this down before is that that's a
> pretty small window. You could force the problem by stopping process B
> with a debugger breakpoint and then letting A do its thing, but short of
> something like that you'll never reproduce it with high probability.
>
> As far as Andrew's question goes: I have no doubt that this race
> condition is (or now, was) real and could explain Stefan's failure.
> It's not impossible that there's some other problem in there, though.
> If so we will still see the problem from time to time on HEAD, and
> know that we have more work to do. But I don't think that continuing
> to see it on the back branches will teach us anything.
maybe the following buildfarm report means that we need a new theory :-(
http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=sponge&dt=2006-08-16%2021:30:02
Stefan
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