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

From: Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Josh Berkus <josh(at)agliodbs(dot)com>, 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 10:35:50
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> As things stand, though, I think the only thing that's really open for
> discussion is how wide to make the scope of the default-change: should
> we just do it across the board, or try to limit it to some subset of the
> platforms where open_datasync is currently the default.  And that's a
> decision that ought to be informed by some performance testing.

Maybe I have a distorded view of the situation for having hit the
problem with an ubuntu upgrade, but it really does not look like a
performance item to me.

PANIC:  could not open file "pg_xlog/000000010000000000000001" (log file 0, segment 1): Invalid argument

It took me quite some time to be able to start my development cluster
again and validate some new patch to send to the list.

Now I understand that you want to test the other alternatives before to
choose among those which work, but my opinion is that it should be fixed
in HEAD before next alpha, or even ASAP. It could be that a HINT here
would be enough for contributors not to lose to much time. It would be

HINT: if you're running linux, please try to change wal_sync_method,
open_datasync is not reliable anymore in recent kernels. An example of
trustworthy setting is fdatasync.

Dimitri Fontaine     PostgreSQL : Expertise, Formation et Support

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