Really slow IMAP performance

[Aki Tuomi]

> On 24 February 2018 at 15:47 Neil Jerram <neil at ossau.homelinux.net> wrote:
> 
> 
> 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

You are using mbox format. This is ... bit slow. =)

When you move mails between mbox files, it has to rewrite the entire mbox file every time. You should probably start using maildir or sdbox instead.

Aki