Message-ID: <455991B0.6070209@streppone.it>
Date: Tue, 14 Nov 2006 10:51:44 +0100
From: Cosimo Streppone <cosimo@streppone.it>
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To: Richard Huxton <dev@archonet.com>
CC: Postgresql Performance list <pgsql-performance@postgresql.org>
Subject: Re: Context switch storm
References: <efc1d7c07cf.454afe8d@brturbo.com.br> <454B3B75.6@archonet.com>
	<454B3EDC.3090502@streppone.it> <454B4438.9080105@archonet.com>
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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