quota recalc problem for big maildirs

[Dawid Stawiarski - nazwa.pl]

hi,

we use dovecot 2.2.13, and we've lately started using maildir quota 
(previously fs quota was used, right now it's "quota = maildir:User 
quota" changed from "quota  = fs:User quota:user:inode_per_mail").

When the change was applied we didn't manually forced generating 
maildirsize files. So, when the first deliver happens (or the file grows 
larger then 5KB) it starts quota recalc. However for users with big 
maildirs, receiving email every couple of seconds, there are tens of 
delivery processes each doing its own recalc (as they open file for 
APPEND and there's no locking). What's even worse, after all the stats 
and getdents (it takes a lot of IO for 60GB account with 2M emails), 
deliver makes stat on 'new' dir and detects changes after which it 
unlinks freshly created maildirsize. So possibly this will never be 
finished as every process drops its own work.

The same thing happened when we checked the native dovecot LMTP server 
(every connection has its own forked process - each running 
independently of the others).

Is it a known unwanted "feature" of maildir quota (and we should use 
dict quota instead) or a bug that will be fixed?

cheers,
Dawid Stawiarski