Date: Tue, 13 Jun 2006 17:47:59 -0500
From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Mischa Sandberg <mischa@ca.sophos.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Solaris shared_buffers anomaly?
Message-ID: <20060613224759.GM34196@pervasive.com>
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	<20060613200810.GZ34196@pervasive.com>
	<448F3A6E.6080908@ca.sophos.com>
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On Tue, Jun 13, 2006 at 03:21:34PM -0700, Mischa Sandberg wrote:
> Jim C. Nasby wrote:
> ...
> >Actually, in 8.1.x I've seen some big wins from greatly increasing the
> >amount of shared_buffers, even as high as 50% of memory, thanks to the
> >changes made to the buffer management code. ...
> 
> Anyone else run into a gotcha that one of our customers ran into?
> PG 7.4.8 running on Solaris 2.6, USparc w 4GB RAM.
> Usually about 50 active backends.
> (No reason to believe this wouldn't apply to 8.x).
> 
> Initially shared_buffers were set to 1000 (8MB).
> Then, we moved all apps but the database server off the box.
> 
> Raised shared_buffers to 2000 (16MB).
> Modest improvement in some frequent repeated queries.
> 
> Raised shared_buffers to 16000 (128MB).
> DB server dropped to a CRAWL.
> 
> vmstat showed that it was swapping like crazy.
> Dropped shared_buffers back down again. 
> Swapping stopped.

What's sort_mem set to? I suspect you simply ran the machine out of
memory.

Also, Solaris by default will only use a portion of memory for
filesystem caching, which will kill PostgreSQL performance.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461