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From: Marc Cousin <cousinmarc@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: performance regression with Linux 2.6.33 and glibc 2.12
Date: Fri, 4 Jun 2010 17:29:04 +0200
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Cc: pgsql-performance@postgresql.org
References: <201006041539.03868.cousinmarc@gmail.com>
	<2135.1275659945@sss.pgh.pa.us>
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Message-Id: <201006041729.04321.cousinmarc@gmail.com>

The Friday 04 June 2010 15:59:05, Tom Lane wrote :
> Marc Cousin <cousinmarc@gmail.com> writes:
> > I hope I'm not going to expose an already known problem, but I couldn't
> > find it mailing list archives (I only found
> > http://archives.postgresql.org/pgsql- hackers/2009-12/msg01543.php).
> 
> You sure this isn't the well-known "ext4 actually implements fsync
> where ext3 didn't" issue?
> 
> 			regards, tom lane

Everything is ext4. So I should have fsync working with write barriers on all 
the tests.

I don't think this problem is of the same kind: I think it is really because 
of O_DSYNC appearing on 2.6.33, and PostgreSQL using it by default now. If my 
filesystem was lying to me about barriers, I should take no more performance 
hit with open_datasync than with fdatasync, should I ?