From: Josh Berkus <josh@agliodbs.com>
Organization: PostgreSQL @ Sun
To: pgsql-performance@postgresql.org
Subject: Re: shared_buffers in 8.3 w/ lots of RAM on dedicated PG machine
Date: Fri, 15 Feb 2008 10:06:11 -0800
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Cc: Greg Smith <gsmith@gregsmith.com>,
	Peter Schuller <peter.schuller@infidyne.com>
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On Friday 15 February 2008 06:29, Greg Smith wrote:
> PostgreSQL only uses direct I/O for writing to the WAL; everything else
> goes through the regular OS buffer cache unless you force it to do
> otherwise at the OS level (like some Solaris setups do with
> forcedirectio).

Also, note that even when direct I/O is available, most users and benchmark 
tests have reported that having PostgreSQL "take over" the entire cache is 
not a net performance gain.  I believe this is mostly because our I/O and 
caching code aren't designed for this kind of operation.

I believe that MyEmma had a different experience on their workload, though. 

-- 
Josh Berkus
PostgreSQL @ Sun
San Francisco