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

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Josh Berkus <josh(at)agliodbs(dot)com>
Subject: Re: We really ought to do something about O_DIRECT and data=journalled on ext4
Date: 2010-12-01 19:03:38
Message-ID: 4CF69C0A.8020701@dunslane.net (view raw or flat)
Thread:
Lists: pgsql-hackers

On 12/01/2010 01:41 PM, Andres Freund wrote:
> On Wednesday 01 December 2010 19:09:05 Tom Lane wrote:
>> Josh Berkus<josh(at)agliodbs(dot)com>  writes:
>>> It's a bug and it's our bug.
>> No, it's a filesystem bug that this particular filesystem doesn't
>> support a perfectly reasonable combination of options, and doesn't
>> even fail gracefully as it could easily do.  But assigning blame
>> doesn't help much.
> I wouldnt call it a reasonable combination - promising fs-level data-
> journaling (data=journal) and O_DIRECT are not really compatible with each
> other...
>
>

OK, but how is an application supposed to know that data journaling is 
set. Postgres doesn't even look at the FS type, let alone the mount 
options. From the app's POV it's perfectly reasonable. If the OS is 
going to provide the API, it should expect people to use it.

cheers

andrew

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