Really slow IMAP performance

[Neil Jerram]

Aki Tuomi <aki.tuomi at dovecot.fi> writes:

>  On 24 February 2018 at 12:45 Neil Jerram < neil at ossau.homelinux.net> wrote: 
>
>  Please could you help me to understand and fix why my dovecot IMAP 
>  performance is so bad? I've read through a lot of the 
>  performance-related material on the website, but I don't think that any 
>  of it could account for slowness at the level that I am seeing. 
>
>  The simplest scenario is moving a message from my Inbox to another IMAP 
>  folder. Using Gnus as the client, the whole UI freezes for about 2 
>  minutes (which I assume is until the move is complete), and journalctl 
>  on the dovecot server says: 
>
>  Feb 24 10:24:24 arudy dovecot[1712]: imap(neil): Warning: Transaction log file /home/neil/dovecot-mail/.imap/INBOX/dovecot.index.log was locked for 98 seconds (Mailbox was synchronized) 
>
>  or the same message with (rotating while syncing). 
>
>  There must be something badly wrong in my setup, or perhaps in the spec 
>  of the server that dovecot is running on. What should I look at to 
>  start understanding this better? 
>
>  Many thanks - Neil 
>
> Can you tell a bit more about your environment? Sounds like io issue 

Thanks for your reply.  I'm not sure exactly what you have in mind, but
here are some starting points:

arudy:~# uname -a
Linux arudy 4.13.0-1-686-pae #1 SMP Debian 4.13.4-2 (2017-10-15) i686 GNU/Linux

arudy:~# dovecot -n
# 2.2.32 (dfbe293d4): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.20 (7cd71ba)
# OS: Linux 4.13.0-1-686-pae i686 Debian buster/sid 
auth_mechanisms = plain login
auth_username_format = %Ln
auth_verbose = yes
login_trusted_networks = 192.168.11.8
mail_access_groups = mail
mail_fsync = never
mail_location = mbox:~/dovecot-mail:INBOX=/var/mail/%u
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 {
  driver = pam
}
plugin {
  antispam_backend = dspam
  antispam_dspam_args = --deliver;--user;%u
  antispam_dspam_binary = /usr/bin/dspam
  antispam_signature = X-DSPAM-Signature
  antispam_signature_missing = error
  antispam_spam = Spam
  antispam_trash = trash;Trash;Deleted Items; Deleted Messages
  fts = solr
  fts_solr = url=http://localhost:8080/solr/
  sieve = file:~/sieve;active=~/.dovecot.sieve
}
postmaster_address = postmaster at ossau.homelinux.net
protocols = " imap lmtp"
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0666
    user = postfix
  }
}
service lmtp {
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    group = postfix
    mode = 0600
    user = postfix
  }
}
ssl_cert = </etc/dovecot/cert.pem
ssl_key =  # hidden, use -P to show it
userdb {
  driver = passwd
}
protocol lmtp {
  mail_fsync = optimized
}
protocol lda {
  mail_fsync = optimized
}

arudy:~# cat /proc/cpuinfo 
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 8
model name	: Pentium III (Coppermine)
stepping	: 6
microcode	: 0x8
cpu MHz		: 935.497
cache size	: 256 KB
physical id	: 0
siblings	: 1
core id		: 0
cpu cores	: 1
apicid		: 0
initial apicid	: 0
fdiv_bug	: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 2
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pse36 mmx fxsr sse cpuid
bugs		:
bogomips	: 1870.99
clflush size	: 32
cache_alignment	: 32
address sizes	: 36 bits physical, 32 bits virtual
power management:

arudy:~# free
              total        used        free      shared  buff/cache   available
Mem:         248808       31572        4080        2576      213156      205880
Swap:        763052       20480      742572