Really slow IMAP performance

[Aki Tuomi]

> On 24 February 2018 at 16:04 Neil Jerram <neil at ossau.homelinux.net> wrote:
> 
> 
> Aki Tuomi <aki.tuomi at dovecot.fi> writes:
> 
> >> On 24 February 2018 at 15:47 Neil Jerram <neil at ossau.homelinux.net> wrote:
> 
> [...]
> >> >  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)
> [...]
> 
> > 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.
> 
> Ah, right, thanks.
> 
> My INBOX file has 22990 messages.  Is the slowness that I am seeing
> definitely expected for an mbox of that size?  (It may also be relevant
> that the HDD it's stored on is pretty old now, and has been known to
> report SMART errors...)
> 
> If so, I'll start looking at how to migrate, given that my system is
> Postfix + Dovecot.  If you have any particular recommendations or
> migration pointers for a system like that, I'd appreciate them.
> 
> Best wishes - Neil

Yes. You deffo are looking at several reasons for slowness.

I can only recommend moving into maildir or sdbox format, and probably new HDD too.

https://wiki2.dovecot.org/Tools/Doveadm/Sync here is example of 'converting' between mailbox formats using dsync. You should also read https://wiki2.dovecot.org/Migration/MailFormat

mbox format has been known to act up with dsync occasionally, so I recommend using 

doveadm backup maildir:~/Maildir

if you want to give it a try, instead of doveadm sync. Backup does dsync too, but it only works one way.

Aki