[Dovecot] Improving lmtp performance

[Joseba Torre]

El Thursday 03 February 2011, Stan Hoeppner <stan at hardwarefreak.com> dijo:
> You've posted no log data.  It's pretty difficult to diagnose problems
> without log entries.  Do you just want us to guess?

Yes, I now may mail was pretty vague, but so was the issue. I posted no logs 
because I saw nothing really useful in them; the only sympton was the slow 
delivery rate.

Postfix's was full of messages going to the active queue
Feb  1 12:43:20 server1 postfix/qmgr[8916]: ED7236CDC1: 
from=<noreply at mydomain.com>, size=8314, nrcpt=1 (queue active)
Feb  1 12:43:21 server1 postfix/smtpd[9427]: 289306CDC3: 
client=lgux66.lgp.mydomain.com[10.0.100.71]
Feb  1 12:43:21 server1 postfix/cleanup[12768]: 289306CDC3: message-
id=<moodlepost24182 at moodle2.mydomain.com>
Feb  1 12:43:21 server1 postfix/qmgr[8916]: 289306CDC3: 
from=<noreply at mydomain.com>, size=8313, nrcpt=1 (queue active)

and some occasional delivery
Feb  1 12:43:23 server1 postfix/lmtp[9549]: 0C5866CF37: 
to=<cdmorales001 at server1.mydomain.com>, 
relay=server1.mydomain.com[/var/spool/postfix/private/dovecot-lmtp], 
delay=854, delays=37/668/140/9.8, dsn=2.0.0, status=sent (250 2.0.0 
<cdmorales001 at server1.mydomain.com> upb1FNftR03cIgAAl0Wliw Saved)

or delivery error
Feb  1 12:43:21 server1 postfix/lmtp[9554]: 1C2946CF92: 
to=<aanton007 at server1.mydomain.com>, 
relay=server1.mydomain.com[/var/spool/postfix/private/dovecot-lmtp], 
delay=815, delays=1.6/664/141/8
.9, dsn=4.2.2, status=SOFTBOUNCE (host 
server1.mydomain.com[/var/spool/postfix/private/dovecot-lmtp] said: 552 5.2.2 
<aanton007 at server1.mydomain.com> Quota exceeded (mailbox for user is full) (
in reply to end of DATA command))

(softbounce was activated to prevent bounces because of misconfigurations)

Dovecot's was as usual, with some
Feb  1 13:18:09 server1 dovecot: lmtp(8924, llasa002 at server1.mydomain.com): 
ArX1FNftR03cIgAAl0Wliw: msgid=<CDPMA-WI015feT9L0Yd00060a97 at CDPMA-
WI01.infoempleo.com>: saved mail to INBOX
Feb  1 13:18:22 server1 dovecot: lmtp(8924, aarruti011 at server1.mydomain.com): 
FbX1FNftR03cIgAAl0Wliw: msgid=<moodlepost24217 at moodle2.mydomain.com>: saved 
mail to INBOX
Feb  1 13:18:23 server1 dovecot: lmtp(8924, jlopez078 at server1.mydomain.com): 
E7X1FNftR03cIgAAl0Wliw: msgid=<moodlepost24182 at moodle2.mydomain.com>: saved 
mail to INBOX

(this was the actual delivery rate: in this case, 3 messages in 14 secs)

My question was if this is the expected behavior, or if lmtp was expected to 
behave a lot better with just 1 process (that was what I expected, at least), 
and if my solution was usual or at least correct. It was not a practical 
question -my system is working fine now-, but a more teorical one. I was 
expecting answers like

"I'm using a very simple conf for lmtp in a busy server, something similar to

protocol lmtp {
  mail_plugins = quota sieve
}
service lmtp {
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    group = postfix
    mode = 0660
    user = postfix
  }
}

and it's working fine for me, so look in other place".

> 
> > Also, if this is a common problem, may be something should appear in 
> > http://wiki2.dovecot.org/LMTP
> 
> That's a bit premature.  The problem could just as likely be a Postfix
> configuration error.  Get us some logs from both Postfix and Dovecot for
> the previous configuration with the slow performance.

I agree. That's why a say "if this is a common problem".
> 
> Are both Postfix and Dovecot running in the same VM guest OS instance or
> two separate VM guests?  Are you running elaborate Sieve scripts?  Are you
> running AV/AS in Dovecot?  Anything relatively CPU heavy in Dovecot on a
> per message basis?

Yes, everything was in the same VM guest, no elaborated sieve scripts that I 
know (I've just recreated them with horde's ingo, and I'm sure they are quite 
basic), no AV/AS, and system's load was normal, with some i/o wait, but in my 
experience this is usual in VM guests.

Thanks.
-- 
Joseba Torre. Vicegerencia de TICs, área de Explotación