[Dovecot] Performance problems while running doveadm purge

[Stan Hoeppner]

On 12/7/2012 8:46 AM, Jost Krieger wrote:
> I have a rather large and active mdbox (28 GB, 3M mess, 1200
> deliveries/day). I usually have no problems working with those mails,
> and there is some batch processing going on (via doveadm).
> 
> Every few weeks I try my luck running doveadm purge, and this
> a) crunches about 5GB (to be expected),
> b) takes rather long (ok),
> c) leads to long stretches of blocked mdbox, which is the problem.
> 
> I always turn off the batch processing, but deliveries take so long that
> they sometimes give up after timeout (they will come back later), and
> the IMAP clients get blocked for long minutes. Sometimes even the purge
> run aborts because of 3-minute-timeouts.
> 
> What could be going on here (2.1.10)?

As always "dovecot -n" output would be helpful as well as log entries
showing timeouts or errors.  Knowing your mdbox_rotate_size setting
would be helpful.

Also, are you purging one mailbox at a time, or all of them
simultaneously.  Have you looked at iostat?  It may simply be that
you're running out of random seek bandwidth on your storage device.
I.e. the heads simply aren't fast enough to keep up with the block
requests.  Also, which OS and filesystem are you using?  Again, "dovecot
-n" would have already answered many of these questions.

-- 
Stan