[Dovecot] load increase after upgrade to 2.0.8

[Mark Moseley]

On Thu, Dec 9, 2010 at 12:58 PM, Timo Sirainen <tss at iki.fi> wrote:
> On Thu, 2010-12-09 at 10:18 -0800, Mark Moseley wrote:
>
>> Upping the client_limit actually results in less processes, since a
>> single process can service up to #client_limit connections. When I
>> bumped up the client_limit for imap, my context switches plummeted.
>> Though as Timo pointed out on another thread the other day when I was
>> asking about this, when that proc blocks on I/O, it's blocking all the
>> connections that the process is servicing.
>
> Yeah. And it's even worse if it's blocking on waiting for a lock.
>
> BTW. Do you have these kind of error messages in your log:
>
> net_connect_unix(pop3) failed: Resource temporarily unavailable
> net_connect_unix(imap) failed: Resource temporarily unavailable
>
> I think those are sometimes happening when not using client_limit=1,
> because all the processes are busy at that time and can't accept a new
> connection (while with client_limit=1 a new process would be created to
> handle it).

Yeah, I do get small bursts of those, but not enough to get too
worried about. I was assuming it was hitting process_limit for imap.
On one box, for all of today I see two clusters of those errors, both
lasting about 15-20 seconds apiece.

The problem is that the smaller I set client_limit (including =1) on
imap, the more likely the mass of imap processes will push these box
into swap (and these are old 2gig boxes; hoping to get replace them
soon with newer Dells, like PE 450's).