[Dovecot] POP (dot) locks

Christian Balzer chibi at gol.com
Sat May 22 05:30:46 EEST 2004

Timo wrote:
>So, currently Dovecot doesn't try to lock mbox for the whole POP3
>session. That may create problems if two sessions actually try to access
>the mailbox concurrently. If message gets expunged by another process,
>Dovecot replies with -ERR to requests to fetch the message. That might
>confuse some POP3 clients, or cause them to send errors to user.
That is (for me at least) acceptable as long as there is no danger of
actual mailbox corruption (a message gets deleted while another client is 
actually downloading it). Is this the case in .99.10.4?

Again, just expunging something get some things
confused, but not lethally so, as tested with a number of clients here. ^^
>I don't think normally anyone even tries concurrent POP3 access? 
Unfortunately the harsh reality of ISP life tells us otherwise, at least
with substandard clients on slow links. Typical current scenario:
User with Outlook (Express) on an ISDN or dialup link gets a huge mail.
The default timeout for that client is 1 minute, after that it just gives 
up, but w/o our end actually noticing it. The result are the previously
mentioned 30 minutes of POP-lock until qpopper gives up itself or the 
user tears down the PPP session which gets the message across to qpopper,
too. Now during the server side imposed lock the user will be told that
another POP session is active while that isn't true from their point of 
view of course. With the current dovecot they can try again immediately,
of course failing again on the large email but the consistent error given 
might lead them to the right course of action: Get better software, a 
better link or at least configure your current setup correctly. ;)

>I have thought before that Dovecot/pop3 should lock the mbox for the
>whole time, just like all others POP3 servers do (and RFC says too)..
>I'll add in TODO.
If the RFC requires it, there will be no argument from me, though more
granular locks which prevent really bad things from happening are
sufficient for me and as detailed above might be more responsive.

Also you are saying mbox up there, would a maildir storage accessed via
POP3 really be immune to these possibly confusing effects for clients?


Christian Balzer
Christian Balzer        Network/Systems Engineer                NOC
chibi at gol.com   	Global OnLine Japan/Fusion Network Services

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