[rabbitmq-discuss] rabbitmq causing heavy disk i/o with nothing in the queues

Ceri Storey ceri at lshift.net
Fri Jul 12 10:12:21 BST 2013

(11/07/13 22:08), Matthias Radestock wrote:
> Kevin,
> On 11/07/13 17:38, Kevin Goess wrote:
>> Circling back after an earlier question about this problem. We've
>> upgraded to 3.1.3-1.  We've moved the mnesia files to a dedicated 10k
>> sata drive via RABBITMQ_MNESIA_BASE, a new drive that nothing else is
>> using, on a xen virtual machine that is only running rabbitmq.  We
>> generally deal with about 20 messages per second.
>> But we're seeing pretty heavy disk activity, with iowait 30-40%, and
>> iostat numbers like this:
>> Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s
>> avgrq-sz avgqu-sz   await  svctm  %util
>> xvdbp1            0.00    60.00    0.00  143.40     0.00  1452.80
>>   10.13     0.88    6.14   4.22  60.48
>> Is this expected?  That seems excessive, and I worry that the high
>> iowait could cause us problems as we grow, so I was hoping to get some
>> pointers to things to look at that to improve that.
> My suspicious is that somehow your usage pattern results in a lot of
> queue/exchange/binding creation/deletion, which, if the entities
> involved are durable, require disk writes and fsyncs.
> To test the validity of that theory, please try to find out what files
> are seeing activity, and report back.

FWIW, that can be done with:

inotifywait -rme modify,move,delete,create /var/lib/rabbitmq

(If your rabbitmq directory is elswhere, of course modify to taste). You
might well need to install the inotify-tools package for your distribution.

> Regards,
> Matthias.
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