[Dovecot] High Load Average on POP/IMAP.

Kavish Karkera kavish.karkera at yahoo.com
Wed Aug 21 13:37:46 EEST 2013


Hi,

We have a serious issue running on our POP/IMAP servers these days. The load average of a servers 
spikes up to 400-500  as a uptime command result, for a particular time period , to be specific 
mostly in noon time and evening, but it last for few minutes only.

We have 2 servers running dovecot 1.1.20 , in loadbanlancer, We have used KEEPLIVE (1.1.13) for 
loadbalacing.

Server specification.
Operating System : CentOS 5.5 64bit
CPU cores : 16
RAM : 8GB

Mail and Indexes are mounted on NFS (NetApp).

Below is the dovecot -n ... (top results during high spike)


#############################################################################################

# 1.1.20: /usr/local/etc/dovecot.conf
# OS: Linux 2.6.28 x86_64 CentOS release 5.5 (Final) 
log_path: /var/log/dovecot-info.log
info_log_path: /var/log/dovecot-info.log
syslog_facility: local1
protocols: imap imaps pop3 pop3s
listen(default): *:143
listen(imap): *:143
listen(pop3): *:110
ssl_listen(default): *:993
ssl_listen(imap): *:993
ssl_listen(pop3): *:995
ssl_cert_file: /usr/local/etc/ssl/certs/dovecot.pem
ssl_key_file: /usr/local/etc/ssl/private/dovecot.pem
disable_plaintext_auth: no
login_dir: /usr/local/var/run/dovecot/login
login_executable(default): /usr/local/libexec/dovecot/imap-login
login_executable(imap): /usr/local/libexec/dovecot/imap-login
login_executable(pop3): /usr/local/libexec/dovecot/pop3-login
login_greeting: Welcome to Popserver.
login_process_per_connection: no
max_mail_processes: 1024
mail_max_userip_connections(default): 100
mail_max_userip_connections(imap): 100
mail_max_userip_connections(pop3): 50
verbose_proctitle: yes
first_valid_uid: 99
first_valid_gid: 99
mail_location: maildir:~/Maildir:INDEX=/indexes/%h:CONTROL=/indexes/%h
mmap_disable: yes
mail_nfs_storage: yes
mail_nfs_index: yes
lock_method: dotlock
mail_executable(default): /usr/local/libexec/dovecot/imap
mail_executable(imap): /usr/local/libexec/dovecot/imap
mail_executable(pop3): /usr/local/libexec/dovecot/pop3
mail_plugins(default): quota imap_quota
mail_plugins(imap): quota imap_quota
mail_plugins(pop3): quota
mail_plugin_dir(default): /usr/local/lib/dovecot/imap
mail_plugin_dir(imap): /usr/local/lib/dovecot/imap
mail_plugin_dir(pop3): /usr/local/lib/dovecot/pop3
pop3_no_flag_updates(default): no
pop3_no_flag_updates(imap): no
pop3_no_flag_updates(pop3): yes
pop3_lock_session(default): no
pop3_lock_session(imap): no
pop3_lock_session(pop3): yes
pop3_client_workarounds(default): 
pop3_client_workarounds(imap): 
pop3_client_workarounds(pop3): outlook-no-nuls
lda:
  postmaster_address: admin at research.com
  mail_plugins: cmusieve quota mail_log
  mail_plugin_dir: /usr/local/lib/dovecot/lda
  auth_socket_path: /var/run/dovecot/auth-master
auth default:
  worker_max_count: 15
  passdb:
    driver: sql
    args: /usr/local/etc/dovecot-mysql.conf
  userdb:
    driver: sql
    args: /usr/local/etc/dovecot-mysql.conf
  userdb:
    driver: prefetch
  socket:
    type: listen
    client:
      path: /var/run/dovecot/auth-client
      mode: 432
      user: nobody
      group: nobody
    master:
      path: /var/run/dovecot/auth-master
      mode: 384
      user: nobody
      group: nobody
plugin:
  quota_warning: storage=95%% /usr/local/bin/quota-warning.sh 95 %u
  quota_warning2: storage=80%% /usr/local/bin/quota-warning.sh 80 %u
  quota: maildir:storage=64 
##############################################################################################

##############################################################################################

top - 12:08:31 up 206 days, 10:45,  3 users,  load average: 189.88, 82.07, 55.97
Tasks: 771 total,   1 running, 767 sleeping,   1 stopped,   2 zombie
Cpu(s):  8.3%us,  7.6%sy,  0.0%ni,  8.3%id, 75.0%wa,  0.0%hi,  0.8%si,  0.0%st
Mem:  16279824k total, 11913788k used,  4366036k free,   334308k buffers
Swap:  4192956k total,        0k used,  4192956k free, 10359492k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                 
  408 mysql     18   0  384m  38m 4412 S 52.8  0.2  42221:44 mysqld                                                                   
29326 nobody    15   0 22688  10m 1112 D  3.9  0.1   0:00.05 imap                                                                     
29313 nobody    16   0 14892 4892 1000 S  3.1  0.0   0:00.07 imap                                                                     
28129 nobody    16   0 23688 4148 1140 S  2.3  0.0   0:00.10 imap                                                                     
28936 nobody    16   0 25048  13m 1108 S  2.3  0.1   0:00.06 imap                                                                     
29302 nobody    16   0 15168 3924 1000 S  2.3  0.0   0:00.05 imap                                                                     
29307 nobody    16   0 12864 2892 1000 S  2.3  0.0   0:00.03 imap                                                                     
21956 root      15   0 13272 1652  800 R  1.6  0.0   0:06.46 top                                                                      
29119 nobody    16   0 26000 9324 1096 D  1.6  0.1   0:00.11 imap                                                                     
29158 nobody    16   0 12684 2728 1028 S  1.6  0.0   0:00.03 imap                                                                     
29204 nobody    16   0 14400 4232 1000 S  1.6  0.0   0:00.08 imap                                                                     
29262 nobody    16   0 25436 2776 1120 S  1.6  0.0   0:00.02 imap                                                                     
 3397 root      10  -5     0    0    0 S  0.8  0.0  28:02.90 rpciod/2                                                                 
 3401 root      10  -5     0    0    0 S  0.8  0.0 337:30.77 rpciod/6                                                                 
 4218 root      16   0  8948 1548  588 S  0.8  0.0   8:05.53 dovecot                                                                  
10214 root      15   0 50868 1968 1468 S  0.8  0.0   0:30.08 dovecot-auth                                                             
27454 nobody    16   0 19220 5048 1256 D  0.8  0.0   0:00.17 imap                                                                     
27820 nobody    16   0 18916 4704 1252 D  0.8  0.0   0:00.08 imap                                                                     
27925 nobody    16   0 11180 1524 1000 S  0.8  0.0   0:00.07 imap                                                                     
28094 nobody    16   0 11536 2068 1148 S  0.8  0.0   0:00.13 imap                                                                     
28150 nobody    16   0 12528 2396 1104 S  0.8  0.0   0:00.08 imap                                                                     
28196 nobody    16   0 13976 3792 1148 S  0.8  0.0   0:00.21 imap                                                                     
28292 nobody    16   0 11984 1808 1004 S  0.8  0.0   0:00.04 imap                                                                     
28343 nobody    16   0 11584 2052 1152 D  0.8  0.0   0:00.02 imap                                                                     
28352 nobody    15   0 11108 1492 1004 S  0.8  0.0   0:00.04 imap                                                                     
28413 nobody    16   0 11220 1568  996 S  0.8  0.0   0:00.02 imap                                                                     
28434 nobody    16   0 12492 2444 1004 S  0.8  0.0   0:00.05 imap                                                                     
28467 nobody    16   0 11852 2044 1004 D  0.8  0.0   0:00.06 imap                                                                     
28558 nobody    16   0 11904 2316 1168 S  0.8  0.0   0:00.02 imap                                                                     
28643 nobody    16   0 11312 1688 1000 S  0.8  0.0   0:00.04 imap                                                                     
28711 nobody    15   0 12048 1868 1004 S  0.8  0.0   0:00.04 imap                                                                     
28779 nobody    16   0 23392  10m 1000 D  0.8  0.1   0:00.05 imap

############################################################################################

Regards,
Kavish Karkera


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