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Re: PG Killed by OOM Condition

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: daveg <daveg(at)sonic(dot)net>
Cc: Bruno Wolff III <bruno(at)wolff(dot)to>, mark(at)mark(dot)mielke(dot)cc,John Hansen <john(at)geeknet(dot)com(dot)au>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: PG Killed by OOM Condition
Date: 2005-10-25 13:24:04
Message-ID: 13155.1130246644@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
daveg <daveg(at)sonic(dot)net> writes:
> I work with a client that runs 16Gb memory with 16Gb of swap on dual opterons
> dedicated to postgres. They have large tables and like hash joins as they are
> often the fastest way to a result, so work_mem is set fairly large. Sometimes
> postgres is very inaccurate predicting real memory use verses work_mem and
> will grow very much larger than expected.

FWIW, 8.1 should be a lot better at this --- it can dynamically readjust
the hash join parameters to keep memory usage under the work_mem limit.

> When this happens the machine runs out of memory and swap. Without the oom
> killer it simply hangs the machine which is inconvenient as it is at a remote
> location.

It shouldn't "hang" in any case ... something wrong there.  I can
believe that the machine would go to its knees as it thrashes more
and more while approaching the totally-out-of-swap point, but it
shouldn't hang up.  You might have a kernel bug to deal with.

			regards, tom lane

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