[Dovecot] Dovecot I/O scheduling (all versions)

[mikkel at euro123.dk]

I have experienced this on all versions of Dovecot that I’ve used (1.0 -
1.1b6) using IMAP (it’s difficult to test if it’s also there with POP3).

What I see is that if there is a peak in disk usage at the time of a
specific request that requests stalls.
The saturation of disk I/O is momentary but when it’s done (maybe after
one or two seconds) Dovecot still waits for its I/O operation instead of
continuing as soon as resources are available.

Now, I would expect Dovecot to only wait until there are resources
available and not stall for at long time (sometimes it stalls for like 10
seconds, and sometimes completely).

This could be OS specific (I’m using ZFS and Solaris 10 on Sparc) but it
may also be due to the way dovecot is programmed.
There’s always plenty of RAM and CPU available so that’s not what’s
causing troubles.

Is anyone else familiar with this issue?

Regards, Mikkel