Date: Fri, 18 Jan 2008 09:41:21 -0300
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Adrian Moisey <adrian@careerjunction.co.za>
Cc: pgsql-performance@postgresql.org
Subject: Re: strange pauses
Message-ID: <20080118124121.GA5326@alvh.no-ip.org>
References: <478DDF83.8070106@careerjunction.co.za>
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	<4790863E.4000309@careerjunction.co.za>
	<47909577.4070704@careerjunction.co.za>
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Adrian Moisey wrote:
> Hi
>
>>>> If I tail the logs, I see a steady stream of functions that took longer 
>>>> then 5 seconds.  But every now and then I see nothing for 3 minutes and 
>>>> after that a whole bunch (about 20 - 30) queries all finishing at the 
>>>> same second.
>>>
>>> Search this list for references to "checkpoints". If you run 
>>> vmstat/iostat for a bit you should see bursts of disk activity at those 
>>> times.
>>>
>>> Counter-intuitively you probably want *more* checkpoints (with less data 
>>> to write out each time), but see the list archives for discussion. Also 
>>> check the manuals for some background info.
>>
>> We use a lot of checkpoints in our database, we don't care about these 
>
> We use a lot of temporary tables in our database, sorry.
>
>> much.  We think this is causing the checkpoint to write a lot of data at 
>> checkpoint time.  Can we stop this behavior ?

No, data written in temp tables do not cause extra I/O on checkpoint.
Catalog changes due to temp table creation could, but I doubt that's the
problem.

Perhaps, if you want to avoid I/O caused by temp tables (but it's not at
checkpoint time, so perhaps this has nothing to do with your problem),
you could try raising temp_buffers.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support