From mboxrd@z Thu Jan  1 00:00:00 1970
From: jim owens <jowens@hp.com>
Subject: Re: [rfc] fsync_range?
Date: Wed, 21 Jan 2009 16:23:58 -0500
Message-ID: <4977926E.30703@hp.com>
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Cc: Chris Mason <chris.mason@oracle.com>, Theodore Tso <tytso@mit.edu>,
	Nick Piggin <npiggin@suse.de>, linux-fsdevel@vger.kernel.org,
	Eric Sandeen <sandeen@sandeen.net>
To: Jamie Lokier <jamie@shareable.org>
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Jamie Lokier wrote:
> 
> Does O_DIRECT on btrfs still allocate new data blocks?
> That's not very direct :-)
> 
> I'm thinking if O_DIRECT is set, considering what's likely to request
> it, it may be reasonable for it to mean "overwrite in place" too
> (except for files which are actually COW-shared with others of course).

O_DIRECT for databases is to bypass the OS file data cache.

Those (oracle) who have long experience with it on unix
know that the physical storage location can change on
a filesystem.

I do not think we want to make a special case,
it should be up to the db admin to choose cow/nocow
because if they want SNAPSHOTS they need cow.

jim