linux-kernel - Re: [PATCH 0/3] Ext3 latency improvement patches

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Message-ID: <72dbd3150903271724n5e7900a5j2486707565cd9d74@mail.gmail.com>
Date:	Fri, 27 Mar 2009 17:24:54 -0700
From:	David Rees <drees76@...il.com>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Theodore Tso <tytso@....edu>, Jan Kara <jack@...e.cz>,
	Chris Mason <chris.mason@...cle.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 0/3] Ext3 latency improvement patches

On Fri, Mar 27, 2009 at 5:14 PM, Jeff Garzik <jeff@...zik.org> wrote:
> Theodore Tso wrote:
>> OTOH, the really big databases will tend to use direct I/O, so they
>> won't be dirtying the page cache anyway.  So maybe it's not worth the
>
> Not necessarily...  From what I understand, a lot of the individual
> low-level components in cloud storage, such as GoogleFS's chunk server[1] do
> not bypass the page cache, even though they do care about the details of
> data caching and data consistency.

PostgreSQL does not use direct I/O, either (except for the
write-ahead-logs which are written sequentially and only get read
during database recovery).  I'm sure that most of MySQL's database
engines, also don't.

-Dave
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