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Re: Occasional giant spikes in CPU load

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Craig James <craig_james(at)emolecules(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Occasional giant spikes in CPU load
Date: 2010-06-25 14:47:10
Message-ID: 2286.1277477230@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Craig James <craig_james(at)emolecules(dot)com> writes:
> On 6/24/10 9:04 PM, Tom Lane wrote:
>> sinval queue overflow comes to mind ... although that really shouldn't
>> happen if there's "no real load" on the server.  What PG version is
>> this?

> 8.3.10.  Upgraded based on your advice when I first asked this question.

Any chance of going to 8.4?  If this is what I suspect, you really need
this 8.4 fix:
http://archives.postgresql.org/pgsql-committers/2008-06/msg00227.php
which eliminated the thundering-herd behavior that previous releases
exhibit when the sinval queue overflows.

If you're stuck on 8.3 then you are going to have to modify your
application's behavior to eliminate sinval overflows.  If the overall
system load isn't high then I would have to guess that the problem is
some individual sessions sitting "idle in transaction" for long periods,
long enough that a number of DDL operations happen elsewhere.

You could also consider throwing memory at the problem by raising the
sinval queue size.  That'd require a custom build since it's not exposed
as a configurable parameter, but it'd be a one-line patch I think.

Or you could look at using connection pooling so you don't have quite
so many backends ...

			regards, tom lane

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Subject: Re: sudden spurt in swap utilization (was:cpu bound postgresql setup.)
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Subject: Re: sudden spurt in swap utilization (was:cpu bound postgresql setup.)

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