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

> 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