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

Matthias Radestock matthias at rabbitmq.com
Thu Jul 11 22:08:58 BST 2013


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.



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