To: Patric de Waha <lists@p-dw.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Two questions.. shared_buffers and long reader issue 
In-reply-to: <4694F8C5.2040005@p-dw.com> 
References: <4694F8C5.2040005@p-dw.com>
Comments: In-reply-to Patric de Waha <lists@p-dw.com>
	message dated "Wed, 11 Jul 2007 17:35:33 +0200"
Date: Wed, 11 Jul 2007 12:57:42 -0400
Message-ID: <27288.1184173062@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Patric de Waha <lists@p-dw.com> writes:
>    Postgres is running on a dedicated server  P4 DualCore, 4 Gig Ram.

When you don't even mention your disk hardware, that's a bad sign.
In a database server the disk is usually more important than the CPU.

>    Why do long readers influence the rest of the transactions in such a 
> heavy way?
>    Any configuration changes which can help here?
>    Is it a disc-IO bottleneck thing?

Very possibly.  Have you spent any time watching "vmstat 1" output
to get a sense of whether your I/O is saturated?

> WAL files are located on another disc than the dbase itself.

That's good, but it only relates to update performance not SELECT
performance.

> effective_cache_size = 5000     

That's way too small for a 4G machine.  You could probably stand to
boost maintenance_work_mem too.  However, neither of these have any
immediate relationship to your problem.

			regards, tom lane