[Dovecot] Stale imap processes

[Fran Fabrizio]

> kqueue is BSD-specific feature, so you can't use it with Linux.

Ah, I see now.

> But I'd like to know what exactly does "stale processes" mean: Do you
> use SSL and they're all SSL connections? 

Yes, they could all be SSL connections.  Many certainly are, not sure if 
-all- of the stale ones are yet.

> Are they eating any CPU at all?

top reports 0% CPU.

> If you strace them, does it show if they're doing anything? 

Just polling...

gettimeofday({1154640050, 545868}, {300, 0}) = 0
gettimeofday({1154640050, 546099}, NULL) = 0
poll([{fd=6, events=POLLIN|POLLPRI|POLLERR|POLLHUP|POLLNVAL}, {fd=2, 
events=POLLERR|POLLHUP|POLLNVAL}, {fd=5, 
events=POLLIN|POLLPRI|POLLERR|POLLHUP|POLLNVAL}, {fd=0, 
events=POLLIN|POLLPRI|POLLERR|POLLHUP|POLLNVAL}], 4, 0) = 0
gettimeofday({1154640050, 546512}, {300, 0}) = 0
gettimeofday({1154640050, 546725}, NULL) = 0
poll([{fd=6, events=POLLIN|POLLPRI|POLLERR|POLLHUP|POLLNVAL}, {fd=2, 
events=POLLERR|POLLHUP|POLLNVAL}, {fd=5, 
events=POLLIN|POLLPRI|POLLERR|POLLHUP|POLLNVAL}, {fd=0, 
events=POLLIN|POLLPRI|POLLERR|POLLHUP|POLLNVAL}], 4, 531) = 0

...and so on.

> How long are
> they stuck, or don't they ever die?

Until I kill them manually.

> How exactly do you know they are stale? 

Because the clients have been closed and the user owning the process 
does not have any mail applications open.

> Are you sure there aren't any
> clients that still have active connections to it?

Pretty sure - of course it could be the client shutting down uncleanly. 
  Mostly 1.5.0.x of Thunderbird and squirrelmail-1.4.6-5.fc5 with an 
occasional pine user.

The symptom for me is either user's IMAP operation times out or just 
user slowdown.  The resolution is that once I kill the old processes 
owned by that user, their performance immediately improves.  Typical 
example is that user is trying to delete a message from the INBOX (i.e. 
move a message from INBOX to Trash in our Maildir environment). 
Thunderbird will just hang on it, or take 1 minute+ to move the message. 
  If I kill the old imap processes, it seems that the move happens very 
quickly (~ 1 second) if the user tries again immediately thereafter.

-Fran



-- 
Fran Fabrizio
Senior Systems Analyst
Department of Computer and Information Sciences
University of Alabama at Birmingham
http://www.cis.uab.edu/
205.934.0653