[Dovecot] Auth processes/login processes count

[Thomas Hummel]

Hello Timo,

I'm running dovecot-1.2.12/Maildir/LDAP-passdb/LDAP-prefetched-userdb and I'm
experiencing "random" latency (which even seem to make squirrelmail timeout
sometimes) at login without noticing particular load on the server.

LDAP backends are running fine as far as I know so I was investigating maybe
mistuned limits :

Dovecot is configured (for ~3000 users) with

  . each login processed in its own process :

      #login_process_per_connection = yes
      #login_max_connections = 256

   . counts as :

      #login_processes_count = 3
      login_max_processes_count = 1024

      auth default {
      [...]
      count = 5
      }

I've got several questions :

1) how can I count more than login_max_processes_count processes ?

  # ps aux | egrep -i '(pop3|imap)-login' | wc -l
  # 1031

2) could be my auth process count the bottleneck ?
   is there a rule of thumb to deduce it from the login process count ?

3) on dovecot login/master/auth design, is my understanding correct ?

- dovecot-1.2.x :

  . passdb and userdb lookup are done by the auth process, on behalf of either the
    login process which wants to know if the client's password is correct or of the
    master process which wants to check if it was actually correct and which wants
    to have the userdb info.

  . client connection fd is sent to the master which creates the mail process and
    transfers the fd to it.

- dovecot-2.x :

  . client connection fd does not go through the master anymore but through a socket in the login/ directory

  . it's the mail process which ask the auth process for the userdb lookup 

4) with LDAP backend using {CRYPT} passwords dans with plaintext auth enabled in dovecot,
   is the clear password crypted before comparing it to the LDAP crypted password
   or does dovecot try to simply bind to LDAP with the clear password ?

Thanks

-- 
Thomas Hummel 	    | Institut Pasteur
<hummel at pasteur.fr> | Groupe Exploitation et Infrastructure