From: Cosimo Streppone <cosimo@streppone.it>
To: Richard Huxton <dev@archonet.com>
Cc: Postgresql Performance list <pgsql-performance@postgresql.org>
Subject: Re: Context switch storm
Date: Tue, 14 Nov 2006 10:51:44 +0100
Message-ID: <455991B0.6070209@streppone.it> (raw)
In-Reply-To: <454B4438.9080105@archonet.com>
References: <efc1d7c07cf.454afe8d@brturbo.com.br>
<454B3B75.6@archonet.com>
<454B3EDC.3090502@streppone.it>
<454B4438.9080105@archonet.com>
Richard Huxton wrote:
> Cosimo Streppone wrote:
>> Richard Huxton wrote:
>>
>>>> The average context switching for this server as vmstat shows is 1
>>>> but when the problem occurs it goes to 250000.
>>>
>> I seem to have the same exact behaviour for an OLTP-loaded 8.0.1 server
>
> upgrade from 8.0.1 - the most recent is 8.0.9 iirc
> [...]
> Are you seeing a jump in context-switching in top? You'll know when you
> do - it's a *large* jump. That's the key diagnosis. Otherwise it might
> simply be your configuration settings aren't ideal for that workload.
>
Sorry for the delay.
I have logged vmstat results for the last 3 days.
Max context switches figure is 20500.
If I understand correctly, this does not mean a "storm",
but only that the 2 Xeons are overloaded.
Probably, I can do a good thing switching off the HyperThreading.
I get something like 12/15 *real* concurrent processes hitting
the server.
I must say I lowered "shared_buffers" to 8192, as it was before.
I tried raising it to 16384, but I can't seem to find a relationship
between shared_buffers and performance level for this server.
> Well, the client I saw it with just bought a dual-opteron server and
> used their quad-Xeon for something else. However, I do remember that 8.1
> seemed better than 7.4 before they switched. Part of that might just
> have been better query-planning and other efficiences though.
An upgrade to 8.1 is definitely the way to go.
Any 8.0 - 8.1 migration advice?
Thanks.
--
Cosimo
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To: pgsql-performance@postgresql.org
Cc: cosimo@streppone.it, dev@archonet.com
Subject: Re: Context switch storm
In-Reply-To: <455991B0.6070209@streppone.it>
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