[Dovecot] best way to activate quota

[Gábor Lénárt]

On Wed, Sep 12, 2012 at 01:28:58AM +0300, Timo Sirainen wrote:
> Activating quota is equally slow, because it needs to scan sizes of all
> files.  If the size is stored in maildir filename (,S=123) this is pretty
> fast, otherwise it's pretty slow because Dovecot stat()s the files, but
> afterwards it stores them to dovecot-uidlist file.  So the main difference
> is that Maildir++ requires rescanning the quota periodically, while dict
> quota never rescans unless you run doveadm quota rescan.

Ahaa, thanks for your answer.

But ... why is rescan needed sometimes with maildir++? If I don't touch
maildir by other softwares ever (I even have maildir_very_dirty_syncs = yes)
just dovecot pop3/imap and incoming mails via dovecot's lmtp (no other MDAs,
not even the LDA, etc), then why is it needed to rescan periodically with
maildir?  I don't really understand the difference then which needs quota
rescan with maildir++ but not with dict quota during the very same usage
environment otherwise.

Anyway I guess, having dict quota with SQL backend is not so a bad idea: I
would be able to check incoming mails (at MXs) if target user will have
enough space to hold the mail by using the mail size and quota usage (from
SQL what dict quota uses as well) on the MXs using eg postfix policy server
... So I won't generate ugly NDRs later, after accepted mails. Not 100%
accurate (quota usage may change while mail hits dovecot) but at least it
will stop the majority of those quota related NDRs I have problems with
currently.

The only thing which keep me away from dict quota with sql backend that it
needs much more complex stuff than simply using maildir++ quota, but it's
maybe only my lazyness ...

thanks again.