[Dovecot] POP3 Performance

[Steve Campbell]

On 3/16/2012 7:07 AM, Mauricio López Riffo wrote:
> 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

It doesn't seem to matter what type of hardware you might have, NFS can 
cause real bottlenecks, even to the point that your machine may report 
disk errors.

Unfortunately, it's an evil necessity in some shops, but any way to 
eliminate NFS when large throughput is occurring will definitely help. 
Make sure you're running the latest version of NFS on all machines since 
V3 and V4 don't always like each other.

I don't have a solution for it's replacement other than expensive 
hardware solutions.

steve