dovecot - Jan 2009 - Concurrent POP3 Sessions Issues

Hi,

	I have problems with dovecot + ldap + nfs, we could't have more than
20 concurrent sessions of pop3, when user 21 comes, the auth process takes
more than 1 sec and is incresing (while most users arrives, more delay in
autenticacion exists) and my customers complaint about the service.  We need
support about 200 concurrents pop3 users, here is my details

Front Internet
1 Load Balancer configured with 2 servers reals

App Servers
2 Servers Xeon 3.0Ghz, 4G Ram, rhel4 update 7
Dovecot 1.1.8 (i386 rpm complied by source rpm from fedora core 10)

Ldap Server
2 Server Xeon QuadCore 2.5Ghz, 8G Ram, rhel5 update 2
Openldap 2.0.X (x86_64 rpms compiled by source rpm from rhel3)

Nfs Server
1 Server Xeon 3.0Ghz, 4G Ram, rhel3 update 4

My conf:

# 1.1.8: dovecot.conf
# OS: Linux 2.6.9-78.0.13.ELsmp i686 Red Hat Enterprise Linux ES release 4
(Nahant Update 7) 
protocols: imap pop3
listen(default): app-server:143
listen(imap): app-server:143
listen(pop3): app-server:110
ssl_disable: yes
login_dir: /var/run/dovecot/login-mail
login_executable(default): /usr/libexec/dovecot/imap-login
login_executable(imap): /usr/libexec/dovecot/imap-login
login_executable(pop3): /usr/libexec/dovecot/pop3-login
login_greeting: Welcome POP3/IMAP Server New on app1.
login_process_per_connection: no
login_process_size: 256
login_processes_count: 50
mail_max_userip_connections(default): 50
mail_max_userip_connections(imap): 50
mail_max_userip_connections(pop3): 10
verbose_proctitle: yes
first_valid_uid: 8
mail_uid: 8
mail_gid: 12
mail_location:
maildir:%h/Maildir:INDEX=/var/cache/dovecot/indexes/%2d/%1u/%2u/%u
mail_debug: yes
mail_full_filesystem_access: yes
mmap_disable: yes
mail_nfs_storage: yes
mail_executable(default): /usr/libexec/dovecot/imap
mail_executable(imap): /usr/libexec/dovecot/imap
mail_executable(pop3): /usr/libexec/dovecot/pop3
mail_plugins(default): quota imap_quota
mail_plugins(imap): quota imap_quota
mail_plugins(pop3): quota mail_log
mail_plugin_dir(default): /usr/lib/dovecot/imap
mail_plugin_dir(imap): /usr/lib/dovecot/imap
mail_plugin_dir(pop3): /usr/lib/dovecot/pop3
pop3_uidl_format(default): %08Xu%08Xv
pop3_uidl_format(imap): %08Xu%08Xv
pop3_uidl_format(pop3): UID%u-%v
pop3_client_workarounds(default): 
pop3_client_workarounds(imap): 
pop3_client_workarounds(pop3): outlook-no-nuls
auth default:
  realms: domain.cl
  default_realm: domain.cl
  verbose: yes
  debug: yes
  debug_passwords: yes
  count: 32
  worker_max_count: 16
  passdb:
    driver: ldap
    args: /etc/dovecot/dovecot-ldap-new.conf
  userdb:
    driver: ldap
    args: /etc/dovecot/dovecot-ldap-new.conf
plugin:
  quota: maildir
  mail_log_events: delete undelete expunge copy mailbox_delete
  mail_log_fields: uid box msgid size

# dovecot-ldap-new.conf


hosts = 10.1.2.3 10.1.2.4
dn = cn=Usr,o=USERS,c=CL
dnpass = pass
sasl_bind = no
tls = no
auth_bind = yes
ldap_version = 3
base = dc=%d,o=MAIL,o=USERS,c=CL
scope = subtree
user_attrs
mailMessageStore=mail:INDEX=/var/cache/dovecot/indexes/%2d/%1u/%2u/%u,homeDi
rectory=home,,,uidNumber=uid,gidNumber=gid,mailQuota=quota:storage
user_filter = (&(objectClass=posixAccount)(uid=%n))
pass_attrs = mail=user,userPassword=password
pass_filter = (&(objectClass=posixAccount)(uid=%n))
default_pass_scheme = CRYPT


Regards
----

Mauricio L?pez Riffo
Red Hat Certified Engineer 
804006455319519
Netline Telecomunicaciones Chile
Los Conquistadores 2430, Providencia, Santiago.
Codigo Postal: 7530041
Fono: +562 6560600 
M?vil: +569 90992366

On Jan 29, 2009, at 1:17 PM, Mauricio L?pez Riffo wrote:
> 	I have problems with dovecot + ldap + nfs, we could't have more than
> 20 concurrent sessions of pop3, when user 21 comes, the auth process  
> takes
> more than 1 sec and is incresing (while most users arrives, more  
> delay in
> autenticacion exists) and my customers complaint about the service.   
> We need
> support about 200 concurrents pop3 users, here is my details
Someone else was recently complaining about the same thing. Or was it  
you? Anyway, dovecot-auth doesn't know how many users are logged in so  
if the problem really is 21 *concurrent users* instead of n logins/ 
second, I find it highly unlikely that the problem is with  
authentication.

My guess is that this has something to do with NFS. Perhaps start  
Dovecot with strace -tt -f dovecot and then when it's slowing down see  
what syscall it says is blocking.

On Fri, Jan 30, 2009 at 4:39 AM, Mauricio L?pez Riffo
<mauricio.lopez at netline.net> wrote:
> Timo,
>
>        What messages should be see?  I execute the commands and shows a lot
> of messages, i dont know what it means, i m not a programmer :)
>
>
> Thanks
>
> ----
>
> Mauricio L?pez Riffo
> Red Hat Certified Engineer
> 804006455319519
> Netline Telecomunicaciones Chile
> Los Conquistadores 2430, Providencia, Santiago.
> Codigo Postal: 7530041
> Fono: +562 6560600
> M?vil: +569 90992366
>
>> -----Mensaje original-----
>> De: Timo Sirainen [mailto:tss at iki.fi]
>> Enviado el: jueves, 29 de enero de 2009 20:46
>> Para: mauricio.lopez at netline.net; Dovecot Mailing List
>> Asunto: Re: [Dovecot] Concurrent POP3 Sessions Issues
>>
>> On Jan 29, 2009, at 1:17 PM, Mauricio L?pez Riffo wrote:
>>
>> >     I have problems with dovecot + ldap + nfs, we could't have
more than
>> > 20 concurrent sessions of pop3, when user 21 comes, the auth
process
>> > takes more than 1 sec and is incresing (while most users arrives,
more
>> > delay in
>> > autenticacion exists) and my customers complaint about the
service.
>> > We need
>> > support about 200 concurrents pop3 users, here is my details
>>
>> Someone else was recently complaining about the same thing. Or was it
you?
> Anyway,
>> dovecot-auth doesn't know how many users are logged in so if the
problem
> really is 21
>> *concurrent users* instead of n logins/ second, I find it highly
unlikely
> that the problem is
>> with authentication.
>>
>> My guess is that this has something to do with NFS. Perhaps start
Dovecot
> with strace -tt -f
>> dovecot and then when it's slowing down see what syscall it says is
> blocking.
I had the same kind of issues. Moving dovecot to the nfs server
directly solved all my weird problems.