From: Craig James <craig_james@emolecules.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: Occasional giant spikes in CPU load
Date: Fri, 25 Jun 2010 09:16:57 -0700
Message-ID: <4C24D679.7030701@emolecules.com> (raw)
In-Reply-To: <2286.1277477230@sss.pgh.pa.us>
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On 6/25/10 7:47 AM, Tom Lane wrote:
> Craig James<craig_james@emolecules.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.
Yes, there is a chance of upgrading to 8.4.4. I just bought a new server and it has 8.4.4 on it, but it won't be online for a while so I can't compare yet. This may motivate me to upgrade the current servers to 8.4.4 too. I was pleased to see that 8.4 has a new upgrade-in-place feature that means we don't have to dump/restore. That really helps a lot.
A question about 8.4.4: I've been having problems with bloat. I thought I'd adjusted the FSM parameters correctly based on advice I got here, but apparently not. 8.4.4 has removed the configurable FSM parameters completely, which is very cool. But ... if I upgrade a bloated database using the upgrade-in-place feature, will 8.4.4 recover the bloat and return it to the OS, or do I still have to recover the space manually (like vacuum-full/reindex, or cluster, or copy/drop a table)?
> Or you could look at using connection pooling so you don't have quite
> so many backends ...
I always just assumed that lots of backends that would be harmless if each one was doing very little. If I understand your explanation, it sounds like that's not entirely true in pre-8.4.4 releases due to the sinval queue problems.
Thanks,
Craig
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To: pgsql-performance@postgresql.org
Cc: craig_james@emolecules.com, tgl@sss.pgh.pa.us
Subject: Re: Occasional giant spikes in CPU load
In-Reply-To: <4C24D679.7030701@emolecules.com>
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