dovecot - Dec 2012 - Performance problems while running doveadm purge

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)?
 
Jost
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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

On 7.12.2012, at 16.46, 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)?
The purging locks the mdbox only while it's writing to indexes, which should
be a very short duration. The mdbox isn't locked while the m.* files are
being read/written. What 3 minute timeout does purge complain about (exact error
message)? Maybe get a strace output of the purge with "strace -tt -o log
doveadm purge -u user at domain" and grep for SETLK in them to see how long
the locks are being held.