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References: <AANLkTi=hL_-85=daT1WKwdptZrBxuUn=phLUwYPwtVwC@mail.gmail.com>
Date: Wed, 23 Mar 2011 15:41:40 +0100
Subject: Re: buffercache/bgwriter
From: tv@fuzzy.cz
To: "Uwe Bartels" <uwe.bartels@gmail.com>
Cc: pgsql-performance@postgresql.org
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> Hi,
>
> I have very bad bgwriter statistics on a server which runs since many
> weeks
> and it is still the same after a recent restart.
> There are roughly 50% of buffers written by the backend processes and the
> rest by checkpoints.
> The statistics below are from a server with 140GB RAM, 32GB shared_buffers
> and a runtime of one hour.
>
> As you can see in the pg_buffercache view that there are most buffers
> without usagecount - so they are as free or even virgen as they can be.
> At the same time I have 53% percent of the dirty buffers written by the
> backend process.

There are some nice old threads dealing with this - see for example

http://postgresql.1045698.n5.nabble.com/Bgwriter-and-pg-stat-bgwriter-buffers-clean-aspects-td2071472.html

http://postgresql.1045698.n5.nabble.com/tuning-bgwriter-in-8-4-2-td1926854.html

and there even some nice external links to more detailed explanation

http://www.westnet.com/~gsmith/content/postgresql/chkp-bgw-83.htm

regards
Tomas