[Dovecot] Dovecot-auth connection problem

[Alexey Gorbov]

Hello

I have this messages in log:
Jul 29 00:02:56 10.0.4.16 dovecot: imap-login: Can\'t connect to auth server 
at default: Resource temporarily unavailable
Jul 29 00:02:56 10.0.4.16 last message repeated 6 times
Jul 29 00:02:56 10.0.4.16 dovecot: pop3-login: Can\'t connect to auth server 
at default: Resource temporarily unavailable
Jul 29 00:02:56 10.0.4.16 last message repeated 6 times
Jul 29 00:02:56 10.0.4.16 dovecot: imap-login: Can\'t connect to auth server 
at default: Resource temporarily unavailable
Jul 29 00:02:56 10.0.4.16 last message repeated 15 times
Jul 29 00:02:56 10.0.4.16 dovecot: pop3-login: Can\'t connect to auth server 
at default: Resource temporarily unavailable

In this way users can't connect top pop3, imap services. Dovecot restart only 
help me to restore my services. 
I have 80k users  and ~250k sessions per day.
i thank you very much for any valid hint.

Debian Linux 2.6.18-4-686 

dovecot -n output:

# 1.1.2: /etc/dovecot/dovecot.conf
log_timestamp: %Y-%m-%d %H:%M:%S
syslog_facility: local0
protocols: imap pop3
disable_plaintext_auth: no
shutdown_clients: no
login_dir: /var/run/dovecot/login
login_executable(default): /usr/lib/dovecot/imap-login
login_executable(imap): /usr/lib/dovecot/imap-login
login_executable(pop3): /usr/lib/dovecot/pop3-login
login_process_size: 512
login_processes_count: 33
login_max_processes_count: 1000
login_max_connections: 1000
max_mail_processes: 1024
verbose_proctitle: yes
first_valid_uid: 99
mail_location: maildir:%h
mail_debug: yes
mail_executable(default): /usr/lib/dovecot/imap-gaa
mail_executable(imap): /usr/lib/dovecot/imap-gaa
mail_executable(pop3): /usr/lib/dovecot/pop3-gaa
mail_plugin_dir(default): /usr/lib/dovecot/modules/imap
mail_plugin_dir(imap): /usr/lib/dovecot/modules/imap
mail_plugin_dir(pop3): /usr/lib/dovecot/modules/pop3
mail_log_max_lines_per_sec: 0
auth default:
  cache_size: 16384
  cache_ttl: 600
  verbose: yes
  debug: yes
  debug_passwords: yes
  passdb:
    driver: sql
    args: /etc/dovecot/dovecot-sql.conf
  passdb:
    driver: sql
    args: /etc/dovecot/dovecot-sql1.conf
  userdb:
    driver: sql
    args: /etc/dovecot/dovecot-sql.conf
  socket:
    type: listen
   master:
      path: /var/run/dovecot/auth-master
      mode: 511
      user: mail



-- 
Best regards,
Alexey Gorbov
gaa at udmvt.ru