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Re: We really ought to do something about O_DIRECT and data=journalled on ext4

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: We really ought to do something about O_DIRECT and data=journalled on ext4
Date: 2010-12-01 18:19:40
Message-ID: 4CF691BC.4050602@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-hackers
> I think the best answer is to get out of the business of using
> O_DIRECT by default, especially seeing that available evidence
> suggests it might not be a performance win anyway.

Well, we don't have any performance evidence ... there's an issue with
the fsync-test script which causes it not to use O_DIRECT.

However, we haven't seen any evidence for benefits on any production
filesystem, either.  So given the lack of evidence of performance
benefit, combined with the definite evidence of related failures, I
agree that simply disabling O_DIRECT by default would be a good way to
solve this.

It might be nice to add new sync_method options, "osync_odirect" and
"odatasync_odirect" for DBAs who think they know enough to tune with
non-defaults.

-- 
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com

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Next:From: Andres FreundDate: 2010-12-01 18:41:46
Subject: Re: We really ought to do something about O_DIRECT and data=journalled on ext4
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