Dsync replication - delayed replication (Sync lock)

[Daniel Botting]

Hi,

*Our setup:*

Two Debian 10 machines that are setup to replicate mail between them, we 
have round robin DNS setup so a user can connect to either server.

*What should happen:*

Mail is delivered to either server and replicated across straight away 
to their mailbox on the other server so it does not matter which one 
they are connected to they will receive it fairly soon after delivery.

*What actually happens:*

In some instances the user will experience a delayed receipt of messages 
if they are not connected to the server that the message is initially 
delivered to, sometimes the delay is 5/10 minutes, we had a recent 
support ticket submitted where it was over an hour.

Error message seen in mail.err:

Sep  1 10:16:15 <host name> dovecot: 
dsync-local(<username>)<WELSGEERTl8FEAAAZJ7A9A>: Error: Couldn't lock 
/path/to/mailbox/.dovecot-sync.lock: 
fcntl(/path/to/mailbox/.dovecot-sync.lock, write-lock, F_SETLKW) locking 
failed: Timed out after 30 seconds (WRITE lock held by pid 3697)

Process 3697 is dovecot/doveadm-server.

*Doveconf -n output:*

# 2.3.10.1 (a3d0e1171): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.10 (67bf5bd7)
# OS: Linux 4.19.0-10-amd64 x86_64 Debian 10.5
# Hostname: <server hostname>
auth_verbose = yes
default_vsz_limit = 0
doveadm_password = # hidden, use -P to show it
first_valid_gid = 8
first_valid_uid = 8
last_valid_gid = 8
last_valid_uid = 8
lda_mailbox_autocreate = yes
lda_mailbox_autosubscribe = yes
mail_gid = 8
mail_location = maildir:~/Maildir
mail_plugins = " notify replication"
mail_uid = 8
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope 
encoded-character vacation subaddress comparator-i;ascii-numeric 
relational regex im
ap4flags copy include variables body enotify environment mailbox date 
index ihave duplicate mime foreverypart extracttext editheader imapfla
gs
namespace inbox {
   inbox = yes
   location =
   mailbox Drafts {
     special_use = \Drafts
   }
   mailbox Junk {
     special_use = \Junk
   }
   mailbox Sent {
     special_use = \Sent
  }
   mailbox "Sent Messages" {
     special_use = \Sent
   }
   mailbox Trash {
     special_use = \Trash
   }
   prefix =
}
passdb {
   args = /etc/dovecot/dovecot-ldap.conf.ext
   driver = ldap
}
plugin {
   mail_replica = tcps:<server being replicated to>:<port being used>
   sieve = ~/.dovecot.sieve
   sieve_dir = ~/sieve
   sieve_extensions = +editheader +imapflags
}
postmaster_address = postmaster@<domain address>
protocols = " imap sieve pop3"
replication_max_conns = 12
service aggregator {
   fifo_listener replication-notify-fifo {
     user = mail
   }
   unix_listener replication-notify {
     user = mail
   }
}
service auth {
   unix_listener /var/run/dovecot-exim-bridge {
     mode = 0660
     user = Debian-exim
   }
}
service doveadm {
   inet_listener {
     port = <port being used for replication>
     ssl = yes
   }
}
service imap-login {
   inet_listener imap {
     port = 143
   }
   }
   inet_listener imaps {
     port = 993
     ssl = yes
   }
   process_limit = 512
   process_min_avail = 4
   service_count = 1
}
service imap {
   process_limit = 1024
}
service managesieve-login {
   inet_listener sieve {
     port = <sieve port>
   }
   process_min_avail = 1
   service_count = 8
   vsz_limit = 256 M
}
service managesieve {
   process_limit = 1024
}
service replicator {
   process_min_avail = 1
   unix_listener replicator-doveadm {
     mode = 0666
   }
}
ssl = required
ssl_cert = </path/to/ssl/cert/fullchain.pem
ssl_cipher_list = ALL:!LOW:!SSLv2:!EXP:!aNULL
ssl_client_ca_dir = /etc/ssl/certs
ssl_key = # hidden, use -P to show it
ssl_min_protocol = TLSv1.2
userdb {
   args = /etc/dovecot/dovecot-ldap.conf.ext
   driver = ldap
   override_fields = home=/var/mail/%u uid=mail gid=mail
}
protocol lda {
   mail_plugins = " notify replication sieve"
}
protocol imap {
   mail_max_userip_connections = 32
   mail_plugins = " notify replication"
}
protocol sieve {
   mail_max_userip_connections = 10
   managesieve_logout_format = bytes=%i/%o
   managesieve_max_line_length = 65536
}

Kind regards

Daniel

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