Message-ID: <464D6DE1.6040001@archonet.com>
Date: Fri, 18 May 2007 10:12:01 +0100
From: Richard Huxton <dev@archonet.com>
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To: Ralph Mason <ralph.mason@telogis.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Ever Increasing IOWAIT
References: <011b01c798d5$141365a0$3c3a30e0$@mason@telogis.com>
In-Reply-To: <011b01c798d5$141365a0$3c3a30e0$@mason@telogis.com>
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Ralph Mason wrote:
> We have a database running on a 4 processor machine.  As time goes by the IO
> gets worse and worse peeking at about 200% as the machine loads up.
> 
> The weird thing is that if we restart postgres it’s fine for hours but over
> time it goes bad again.
> 
> (CPU usage graph here HYPERLINK
> "http://www.flickr.com/photos/8347741@N02/502596262/"http://www.flickr.com/p
> hotos/8347741@N02/502596262/ )  You can clearly see where the restart
> happens in the IO area

I'm assuming here we're talking about that big block of iowait at about 
4-6am?

I take it vmstat/iostat show a corresponding increase in disk activity 
at that time.

The question is - what?
Does the number of PG processes increase at that time? If that's not 
intentional then you might need to see what your applications are up to.

Do you have a vacuum/backup scheduled for that time? Do you have some 
other process doing a lot of file I/O at that time?

> This is Postgres  8.1.4 64bit.

You'll want to upgrade to the latest patch release - you're missing 5 
lots of bug-fixes there.

-- 
   Richard Huxton
   Archonet Ltd