Message-ID: <3F8E31F5.9020703@colorfullife.com>
Date: Thu, 16 Oct 2003 07:51:49 +0200
From: Manfred Spraul <manfred@colorfullife.com>
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To: Andrew Dunstan <andrew@dunslane.net>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Database Kernels and O_DIRECT
References: <BBB237C0.5B35%jamesr@best.com> <15890.1066232585@sss.pgh.pa.us>
	<3F8DB5D7.1060600@dunslane.net>
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Andrew Dunstan wrote:

>
> I have wondered (somewhat fruitlessly) for several years about the 
> possibilities of special purpose lightweight file systems that could 
> relax some of the assumptions and checks used in general purpose file 
> systems. Such a thing might provide most of the benefits of a 
> "database kernel" without imposing anything extra on the database 
> application layer.

CPU is usually cheap compared to disk io.

There are two things that might be worth looking into:
Oracle released their cluster filesystem (ocfs) as a GPL driver for 
Linux. It might be interesting to check how it performs if used for 
postgres, but I fear that it implicitely assumes that the bulk of the 
caching is performed by the database in user space.
And using O_DIRECT for the WAL logs - the logs are never read.

--
    Manfred