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

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Josh Berkus <josh(at)agliodbs(dot)com>
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 05:31:34
Message-ID: 6263.1291181494@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
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.

			regards, tom lane

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