Strange log message with dovecot-2.3.3

[Christian Pélissier]

Hi,

# dovecot --version
2.3.3 (dcead646b)


# doveinfo
Nombre d'utilisateurs          : 1151
Sockets IMAP                   : 4356
Process dovecot/imap           : 4357
Process dovecot/imap-login     : 1339
Process dovecot/pop3           : 0
Process dovecot/pop3-login     : 0
Process dovecot/auth           : 1
Process dovecot/auth -w        : 2
Process dovecot/anvil          : 1
Process dovecot/log            : 1
Process dovecot/config         : 1
Process dovecot/stats          : 1

Since I am using dovecot 2.3.X I got the following messages

/var/log/dovecot-20180930:Sep 28 17:33:38 balcha dovecot: master:
Warning: service(stats): client_limit (1000) reached, client connections
are being dropped

Users complain the system became slow.

I happen when dovecot/imap process grows above 1000.

With 2.2.X no default were defined (#default_client_limit = 1000) and I
have no such log and no performance problems.


With 2.3.3 I first increase  default_client_limit to 4096

but the following message come again when dovecot/imap grow above
4096


======
Nov  6 12:09:12 balcha dovecot: master: Warning: service(stats):
client_limit (4096) reached, client connections are being dropped
Nov  6 12:09:25 balcha dovecot: imap: Error:
net_connect_unix(/var/run/dovecot//stats-writer) failed: Resource
temporarily unavailable
... many same lines as above
======

Now 8192 solve my problem
default_client_limit = 8192


I don't understand why the first Warning is related to service(stats)
instead of service(imap)
and why the socket stats-writer became temporarily unavailable

# ls -l /var/run/dovecot/stats-writer
srw-rw---- 1 root dovecot 0 Nov  8 02:44 /var/run/dovecot/stats-writer



PS.

# dovecot --version
2.3.3 (dcead646b)


# dovecot -n
# 2.3.3 (dcead646b): /usr/local/dovecot-2.3.3/etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.3 (f018bbab)
# OS: Linux 2.6.32-696.30.1.el6.x86_64 x86_64 Red Hat Enterprise Linux
Server release 6.9 (Santiago) 
# Hostname: balcha.onera
base_dir = /var/run/dovecot/
default_client_limit = 8192  <<< default with dovecot 2.2.X changed to
4096 then 8192
disable_plaintext_auth = no
listen = *
mail_location = maildir:~/Maildir:INDEX=~/Maildir:CONTROL=~/Maildir
mail_plugins = quota
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope
encoded-character vacation subaddress comparator-i;ascii-numeric
relational regex imap4flags copy include variables body enotify
environment mailbox date index ihave duplicate mime foreverypart
extracttext
mbox_write_locks = fcntl
passdb {
  args = %s
  driver = pam
}
plugin {
  quota = maildir:User quota
  quota_grace = 6%%
  quota_rule = ?:storage=6G
  quota_rule2 = Trash:storage=+5%%
  quota_warning = storage=95%% quota-warning 95 %u
  quota_warning2 = storage=80%% quota-warning 80 %u
  sieve = file:~/sieve;active=~/.dovecot.sieve
}
postmaster_address = postmaster at onera.fr
quota_full_tempfail = yes
rejection_reason = Votre message à <%t> est mis en attente; raison : %n%
r
rejection_subject = Message (Objet: %s) mis en attente de livraison
service anvil {
  client_limit = 4299
}
service auth {
  client_limit = 5320
}
service imap-login {
  client_limit = 8192
  process_limit = 4096
}
service imap {
  process_limit = 8192
}
service quota-warning {
  executable = script /usr/local/bin/quota-warning.sh
  unix_listener quota-warning {
    group = root
    mode = 0666
    user = root
  }
  user = root
}
ssl_cert = </usr/local/dovecot/etc/certs/dovecot.pem
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
syslog_facility = local1
userdb {
  driver = passwd
}
protocol lda {
  mail_plugins = quota sieve
}
protocol imap {
  mail_plugins = quota imap_quota
}
protocol pop3 {
  mail_plugins = quota
  pop3_reuse_xuidl = yes
}

-- 
Christian Pélissier
ONERA DSI/ISR BP72 92322 Chatillon CEDEX
 34419