[Dovecot] load increase after upgrade to 2.0.8

[Ralf Hildebrandt]

* Mark Moseley <moseleymark at gmail.com>:
> On Wed, Dec 8, 2010 at 3:03 PM, Timo Sirainen <tss at iki.fi> wrote:
> > On 8.12.2010, at 22.52, Cor Bosman wrote:
> >
> >> 1 server with service_count = 0, and src/imap/main.c patch
> >
> > By this you mean service_count=0 for both service imap-login and service imap blocks, right?
> >
> >
> 
> Speaking from my own experience, the system loads on our dovecot boxes
> went up *substantially* when we upgraded kernels from 2.6.32.x and
> 2.6.33.x to newer ones (late 2.6.35.x and 2.6.36 -- haven't tried
> 2.6.36.1 yet). But I also saw loads on all sort of other types of
> boxes grow when moved to 2.6.35.x and 2.6.36, so it's not necessarily
> dovecot-related. Though you've got plenty to choose from between
> 2.6.27.x and up.

We're on 2.6.32 and the load only goes up when I change dovecot (not
when I change the kernel, which I didn't do so far)
 
> Getting 'imap-login' and 'pop3-login' set to service_count=0 and
> 'pop3' and 'imap' set to service_count=1000 (as per Timo's suggestion)
> helped keep the boxes from spinning into oblivion. To reduce the
> enormous amount of context switches, I've got 'pop3's client_limit set
> to 4. I played around with 'imap's client_limit between 1 and 5 but
> haven't quite found the sweet spot yet. pop3 with client_limit 4 seems
> to work pretty good. That brought context switches down from
> 10,000-30,000 to sub-10,000.

Interesting. Would that spawn a lot of pop3 processes? On the other
hand, almost nobody is using pop3 here

-- 
Ralf Hildebrandt
  Geschäftsbereich IT | Abteilung Netzwerk
  Charité - Universitätsmedizin Berlin
  Campus Benjamin Franklin
  Hindenburgdamm 30 | D-12203 Berlin
  Tel. +49 30 450 570 155 | Fax: +49 30 450 570 962
  ralf.hildebrandt at charite.de | http://www.charite.de