Message-ID: <4642A811.9010703@drivefaster.net>
Date: Wed, 09 May 2007 23:05:21 -0600
From: Dan Harris <fbsd@drivefaster.net>
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To: pgsql-performance@postgresql.org
Subject: Re: Background vacuum
References: <4642A1B3.6030009@swissembedded.com>
In-Reply-To: <4642A1B3.6030009@swissembedded.com>
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Daniel Haensse wrote:
> Dear list,
> 
> I'm running postgres on a tomcat server. The vacuum is run every hour
> (cronjob) which leads to a performance drop of the tomcat applications.
> I played around with renice command and I think it is possible to reduce
> this effect which a renice. The problem is how can I figure out the PID
> of the postmaster performing the vacuum(automated)? Has anybody a nice
> solution to change process priority? A shell script, maybe even for java?
> 

While this may technically work, I think it lacks a key point.  'nice' ( at 
least the versions I'm familiar with ) do not adjust I/O priority.  VACUUM is 
bogging things down because of the extra strain on I/O.  CPU usage shouldn't 
really be much of a factor.

Instead, I would recommend looking at vacuum_cost_delay and the related settings 
to make vacuum lower priority than the queries you care about.  This should be a 
cleaner solution for you.

-Dan