[Dovecot] lmtp-proxying in 2.1 slower than in 2.0.14 ?

[Timo Sirainen]

On 1.2.2013, at 19.00, Jan-Frode Myklebust <janfrode at tanso.net> wrote:

> We upgraded our two dovecot directors from v2.0.14 to dovecot-ee
> 2.1.10.3 this week, and after that mail seems to be flowing a lot
> slower than before. The backend mailstores are untouched, on v2.0.14
> still. After the upgrade we've been hitting process_limit for lmtp a
> lot, and we're struggeling with large queues in the incoming
> mailservers that are using LMTP virtual transport towards our two
> directors.
> 
> I seem to remember 2.1 should have a new lmtp-proxying code. Is there
> anything in this that maybe needs to be tuned that's different from
> v2.0 ? I'm a bit scheptical to just increasing the process_limit for
> LMTP proxying, as  I doubt running many hundreds of simultaneous
> deliveries should work that much better against the backend storage..

Hmm. The main difference is that v2.1 writes temporary files to mail_temp_dir. If that's in tmpfs (and probably even if it isn't), it should still be pretty fast..

Have you checked if there's an increase in disk I/O usage, or system cpu usage?

Or actually .. It could simply be that in v2.0.15 service lmtp { client_limit } default was changed to 1 (from default_client_limit=1000). This is important with the backend, because writing to message store can be slow, but proxying should be able to handle more than 1 client per process, even with the new temporary file writing. So you could see if it helps to set lmtp { client_limit = 100 } or something.