[Dovecot] cannot update mailbox - unable to lock for exclusive access

[Stan Hoeppner]

On 11/12/2012 5:15 AM, 1st WebDesigns wrote:

> Thanks for your replies.  I switched to Dovecot LDA this morning, but
> the issue still persists, albeit logged slightly differently by Dovecot
> now instead of Postfix:
> 
> "save failed to INBOX: Timeout while waiting for lock"
>
> The reason is because some pop3 clients 

Full stop.  This is the first time you've mentioned POP that I recall.
FYI, Dovecot is primarily an IMAP server.  Unless an OP states up front
that he's using primarily POP, everyone assumes IMAP and counsels
accordingly.  You should have stated POP in your first post.  Actually,
you should have included many more details prior to now.  Please post
your complete 'dovecot -n' output.

> are holding their connection for
> 5 or 6 minutes (don't ask me why - and the iPhone seems to be the major
> culprit).

I'm no smartphone POP expert, but old rural tower, poor tower
connection, etc, all cause low data rates, which could cause this.
However, you state this problem cropped up out of nowhere after a distro
upgrade to CentOS 5.  Can you confirm that the problem didn't exist
before the upgrade?  Your definitive answer to this question dictates
the troubleshooting course of action.

> In dovecot.conf I changed:
> 
> mbox_lock_timeout = 300
> 
> to
> 
> mbox_lock_timeout = 600
> 
> Which seems to have helped.  I am unclear if this value only applied to
> Dovecot LDA or if it would have worked previously before switching to
> Dovecot LDA?

This simply changes how long Dovecot will wait to acquire a lock.
Increasing this value simply increases delays, masks the underlying
problem without really helping much.

The only real architectural solution to such a POP/mbox locking problem
due to slow/long client downloads is, as you mentioned, moving to a
lockless mailbox format, such as maildir or sdbox.

Worth noting, we are both/all at fault in the slow progress of this
issue, you for not stating POP up front, and me/us for not asking.

Your 'dovecot -n' output may allow us to help get mbox working a little
better, but the long term solution is very likely moving to maildir/sdbox.

-- 
Stan