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Date: Fri, 15 Feb 2008 07:37:34 -0600
From: Kenneth Marshall <ktm@rice.edu>
To: Peter Schuller <peter.schuller@infidyne.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: shared_buffers in 8.3 w/ lots of RAM on dedicated PG
	machine
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On Fri, Feb 15, 2008 at 01:35:29PM +0100, Peter Schuller wrote:
> Hello,
> 
> my impression has been that in the past, there has been a general
> semi-consensus that upping shared_buffers to use the majority of RAM
> has not generally been recommended, with reliance on the buffer cache
> instead being the recommendation.
> 
> Given the changes that have gone into 8.3, in particular with regards
> to minimizing the impact of large sequential scans, would it be
> correct to say that given that
> 
>   - enough memory is left for other PG bits (sort mems and whatnot else)
>   - only PG is running on the machine
>   - you're on 64 bit so do not run into address space issues
>   - the database working set is larger than RAM
> 
> it would be generally advisable to pump up shared_buffers pretty much
> as far as possible instead of relying on the buffer cache?
> 
> -- 
> / Peter Schuller
> 
> PGP userID: 0xE9758B7D or 'Peter Schuller <peter.schuller@infidyne.com>'
> Key retrieval: Send an E-Mail to getpgpkey@scode.org
> E-Mail: peter.schuller@infidyne.com Web: http://www.scode.org
> 
Peter,

PostgreSQL still depends on the OS for file access and caching. I
think that the current recommendation is to have up to 25% of your
RAM in the shared buffer cache.

Ken