linux-kernel - Re: Sluggish system while copying large files.

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Date:	Mon, 23 Oct 2006 07:29:20 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	Brice Figureau <brice+lklm@...sofwonder.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Sluggish system while copying large files.

On Mon, Oct 23, 2006 at 11:40:05AM +0200, Brice Figureau wrote:
> 
> I'll try the data=writeback mount option. Is it possible to remount the
> partition and change the journal option on a running system?

Not with ext3, sorry.

> 
> > Since mysql is probably triggering tons of fsyncs or O_SYNC writes,
> > you may want to increase the size of the ext3 log.
> 
> Mysql is using O_DIRECT for its datafile. I don't know how it relates to
> the sync things, but I guess that to be truly ACID, it has to fsync the
> files on each transactions.
> How can I increase the ext3 log ?
> Any idea of the size I should use (and what is the default) ?

Even when using O_DIRECT, if the file is extended an FS commit is
triggered to record the extension.
> 
> > If mysql is constantly appending to the files holding your tables, the
> > synchronous writes are more expensive and log intensive.  Check your
> > setup to see if you can manually extend any of those files to avoid
> > constantly growing table files.
> 
> The use of a battery-backed RAID cache should mitigate the sync writes,
> and since our mysql load is quite low, the machine shouldn't definitely
> freeze for seconds while copying files.

Ok, I would start with only doing data=writeback.  That is probably a
big part of the problem.

-chris

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