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

From: Robert Haas <robertmhaas(at)gmail(dot)com>
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 13:50:36
Message-ID: AANLkTimvsoBFnLj97x3BGYrVfaXH4MxDnD+BAXirVJ_=@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Dec 1, 2010 at 12:31 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Josh Berkus <josh(at)agliodbs(dot)com> writes:
>> On 11/30/10 7:09 PM, Tom Lane wrote:
>>> Josh Berkus <josh(at)agliodbs(dot)com> writes:
>>>> Apparently, testing for O_DIRECT at compile time isn't adequate.  Ideas?
>>>
>>> We should wait for the outcome of the discussion about whether to change
>>> the default wal_sync_method before worrying about this.
>
>> Are we considering backporting that change?
>
>> If so, this would be another argument in favor of changing the default.
>
> Well, no, actually it's the same (only) argument.  We'd never consider
> back-patching such a change if our hand weren't being forced by kernel
> changes :-(
>
> 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.

If we could get a clear idea of what performance testing needs to be
done, I suspect we could find some people willing to do it.  What do
you think would be useful?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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