[Dovecot] difference between client_limit and process_limit

Angel L. Mateo amateo at um.es
Wed Jun 13 14:15:00 EEST 2012

On 11/06/12 13:45, Timo Sirainen wrote:
> On 11.6.2012, at 13.19, Angel L. Mateo wrote:
>>> Proxying is done by imap-login process, not imap process. For login processes there are different recommendations.
>> 	What are those recommendations? The ones at http://wiki2.dovecot.org/LoginProcess?
> Yes.
>> 	Let's suppose... I have 4 mainly imap backend servers (but they admit also pop3 connections) with a process_limit of 5120 for service imap (and default_client_limit of 1000 applied to pop3). And I have 2 director servers (configured as active-active behind a load balancer), so I need director servers to handle (more or less) 10240 imap connections.
>> 	What is it better for the director's? Increasing process_limit for imap-login (so each process should handle less connections) or increasing client_limit (less processes handling more connections each)?
> If you increase process_limit to more than the number of CPU cores you have, then you increase the number of context switched done by the kernel, which decreases your performance. So I'd say increase client_limit.
	I'm trying to configure it this way, so I have configure process_limit 
to the number of cores and client_limit big enough to attempt the 
maximum number of connections configured at the backends.

	In my test environment I have configured (this is extracted from 
doveconf -n output):

service imap-login {
   client_limit = 10740
   executable = imap-login director
   process_limit = 1
   process_min_avail = 1

	When I made the first connection, there's no problem, but if I try a 
second while the first is still open, I get:

Jun 13 13:09:12 myotis40 dovecot: master: Warning: service(imap-login): 
client_limit (1) reached, client connections are being dropped

	Why is telling me that client_limit is reached? What client_limit is used?

Angel L. Mateo Martínez
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