From: Josef Bacik <josef@redhat.com>
Subject: Re: Severe slowdown caused by jbd2 process
Date: Fri, 21 Jan 2011 07:59:22 -0500
Message-ID: <20110121125922.GB8949@dhcp231-156.rdu.redhat.com>
References: <1295568782.2459.29.camel@tybalt> <20110121013140.GA8949@dhcp231-156.rdu.redhat.com> <1295601083.5799.3.camel@tybalt>
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Cc: Josef Bacik <josef@redhat.com>, linux-ext4@vger.kernel.org
To: Jon Leighton <j@jonathanleighton.com>
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On Fri, Jan 21, 2011 at 09:11:23AM +0000, Jon Leighton wrote:
> Hi Josef,
> 
> Thanks for the reply.
> 
> On Thu, 2011-01-20 at 20:31 -0500, Josef Bacik wrote:
> > What kind of database is this?  Does it use lots of files?
> 
> This happens with all databases that I test with: sqlite3, mysql and
> postgresql. Which would seem to indicate that the issue is not actually
> related to the databases, but is being made evident by them when they do
> lots of reads/writes. (The jbd2 every 2 seconds thing happens even when
> all database are completely shut down.)
>

Right I'm not trying to blame the database, more trying to get an idea the kind
of IO that they are generating so we can figure out what is being slow.
 
> > When it's being
> > particularly slow could you run
> > 
> > echo w > /proc/sysrq-trigger
> > 
> > a couple of times, spread out.  This will give us an idea of what everybody is
> > doing when things are going slow.  Thanks,
> 
> Cool, I have done that and attached the results. The partition in
> question (the one with the databases on) is /dev/sda4.
>

Hrm so an fsync heavy workload it looks like.  I'll run some fsync tests locally
and see if I can see the kind of slowdowns you are experiencing.  Thanks,

Josef