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Date: Tue, 6 Jul 2010 09:34:48 +1000
From: Dave Chinner <david@fromorbit.com>
Subject: Re: Slow delete
Message-ID: <20100705233448.GB24712@dastard>
References: <AANLkTinPmhJRD3CDdsHtkLFzYd2jF9ee7gPqgO6XBSfl@mail.gmail.com>
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To: Andrei Deftu <andreideftu@gmail.com>
Cc: xfs@oss.sgi.com

On Mon, Jul 05, 2010 at 05:27:44PM +0300, Andrei Deftu wrote:
> Hi,
> 
> As many people have pointed out, xfs is very slow when deleting a
> large number of files. Does anyone has a technical answer to this
> problem? Also, I am interested to know if there is a way to
> temporarily speed up the delete process, regardless of all the other
> parameters.

The technical reason is to do with the architecture of the
transaction and logging subsystem of XFS. The key concept: relogging
of dirty objects. The reason it affects unlinks: removing files
from the same directory modifies the same objects repeatedly (e.g.
the directory btree blocks).

For a detailed explanation of the concept and how delayed logging
takes advantage of it to speed up stuff like deleting a large number
of files, see:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/filesystems/xfs-delayed-logging-design.txt

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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