[Dovecot] POP3 Performance

[Mauricio López Riffo]

Hi,

     We actually have a mail hosting solutions with aprox. 100 thousand 
of email account, where about 90% of a customers use POP3 like email 
configuration.  About a few mounths (we perfomed a lot of migration 
throught mbox email software to Maildir with dovecot) but i can see that 
the performance is very poor and receive complaint about delays of 
autentications of accounts.

The solution lives in Metrocluster Netapp storage, filesystem NFS, 
VMware as a virtualization (the mtas are a virtual machines lives in 
netapp too) about 4T of data mails and a 10G network connection (betwen 
mtas and nfs storage)  All account information work in LDAP plataform 
(two servers in replicated mode, no high average or delays detected in 
this servers)

When the traffic have a peak of 1800 concurrent connections POP3, all of 
service suffer a high load average (about 8 - 20 load average in each 
dovecot) and authenticacion takes about 2 -10 seconds (in low traffic, 
autenticacion takes about 60 miliseconds)

Also, each dovecot instance lives un MTA server CentOS 5.8 x86_64 with 
6G RAM (virtual machine) and share's hardware with a exim instance, like 
a MTA relay system (autenticated relay)

Usage of network have peaks of 80Mbits (all dmz network have 1Gbits of 
bandwith)

Attach of dovecot -n output:

# 2.0.18: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.18-308.1.1.el5 x86_64 CentOS release 5.8 (Final)
auth_debug_passwords = yes
auth_default_realm = portalplata.cl
auth_realms = portalplata.cl
auth_verbose = yes
auth_verbose_passwords = plain
auth_worker_max_count = 100
base_dir = /var/run/dovecot/
debug_log_path = /var/log/dovecot.log
default_process_limit = 200
default_vsz_limit = 512 M
disable_plaintext_auth = no
first_valid_gid = 12
first_valid_uid = 8
lock_method = dotlock
login_greeting = Dovecot mta10
mail_cache_min_mail_count = 5
mail_debug = yes
mail_fsync = always
mail_full_filesystem_access = yes
mail_gid = 12
mail_location = maildir:%h/Maildir:INDEX=/data/cache/indexes/%2d/%1u/%2u/%u
mail_nfs_storage = yes
mail_plugins = " quota"
mail_uid = 8
maildir_copy_with_hardlinks = no
passdb {
   args = /etc/dovecot/dovecot-ldap.conf.ext
   driver = ldap
}
plugin {
   mail_log_events = delete undelete expunge copy mailbox_delete 
mailbox_rename
   mail_log_fields = box from subject
   quota = maildir
}
postmaster_address = mail at mail.com
protocols = imap pop3
sendmail_path = /usr/lib/sendmail
service auth {
   unix_listener auth-userdb {
     mode = 0600
     user = exim
   }
}
service imap-login {
   service_count = 0
}
service imap-postlogin {
   executable = script-login /usr/local/bin/postlogin.sh
   user = root
}
service imap {
   executable = imap imap-postlogin
}
service pop3-login {
   inet_listener pop3s {
     port = 995
     ssl = yes
   }
   service_count = 0
}
service pop3 {
   process_limit = 1024
}
ssl_cert = </etc/pki/dovecot/certs/dovecot.pem
ssl_key = </etc/pki/dovecot/private/dovecot.pem
userdb {
   args = /etc/dovecot/dovecot-ldap.conf.ext
   driver = ldap
}
verbose_proctitle = yes
protocol lmtp {
   mail_plugins = " quota"
}
protocol lda {
   mail_plugins = " quota"
}
protocol imap {
   imap_capability =
   mail_max_userip_connections = 10
   mail_plugins = " quota autocreate notify quota imap_quota mail_log"
   plugin {
     autocreate = Sent Items
     autocreate2 = Spam
     autocreate3 = Drafts
     autocreate4 = Trash
     autosubscribe = Sent Items
     autosubscribe2 = Spam
     autosubscribe3 = Drafts
     autosubscribe4 = Trash
   }
}
protocol pop3 {
   mail_plugins = " quota quota notify mail_log"
   pop3_reuse_xuidl = yes
   pop3_save_uidl = yes
   pop3_uidl_format = %u
}


Output of account information in a LDAP:

# nettester, email.net, MAIL, USERS, cl
dn: uid=nettester,dc=email.net,o=MAIL,o=USERS,c=cl
dc: email.net
mailMessageStore: /export/mdir/3/12/nettester at email.net/Maildir
uid: nettester
cn: nettester at email.net
sn: nettester at email.net
gidNumber: 12
homeDirectory: /export/mdir/3/12/nettester at email.net
mail: nettester at email.net
uidNumber: 8
objectClass: mailUser
objectClass: posixAccount
objectClass: mailSetting
loginShell: /bin/false
description: enable
service: pop3
service: imap
service2: webmail
mailRate: 200
mailQuota: 1024M
deliveryMode: none
mailReplyText: .

Any suggestions? All ideas will be have a good receptions ;)


Pd: Sorry my english

-- 
Mauricio López Riffo
Red Hat Certified Engineer
804006455319519
Administrador de Servicios Internet
Área Ingeniería
Gtd Internet S.A.
http://www.grupogtd.com/
Moneda 920, Oficina 602 - Fono : +562 4139742