Dictionary quota
================

The /dictionary/ quota backend supports both *storage* and *messages* quota
limits. The current quota is kept in a dictionary. Currently the only supported
dictionary backend is MySQL.

The plugin parameter format is 'dict:<quota limits> <dictionary URI>'. For
example:

---%<-------------------------------------------------------------------------
plugin {
  # 10MB and 1000 messages quota limit
  quota = dict:storage=10240:messages=1000 mysql:/etc/dovecot-dict-quota.conf
}
---%<-------------------------------------------------------------------------

However, *the above example won't really work*. This is because it would
require linking all the binaries with MySQL library, which I didn't really want
to do. Currently you'll have to do this via the dictionary proxy (see below).
Actually the performance is better that way anyway, and I don't really see a
reason not to use it.

Example 'dovecot-dict-quota.conf':

---%<-------------------------------------------------------------------------
connect = host=localhost dbname=mails user=sqluser password=sqlpass
table = quota
select_field = current
where_field = path
username_field = username
---%<-------------------------------------------------------------------------

Create the table like this:

---%<-------------------------------------------------------------------------
create table quota (
  username varchar(255) not null,
  path varchar(100) not null,
  current integer,
  primary key (username, path)
);
---%<-------------------------------------------------------------------------

Inaccuracy problems
-------------------

Quota plugin doesn't currently track expunges entirely correctly. If two IMAP
clients do an expunge at the same time, the quota is reduced twice as much. The
other quota backends have the same problem, but it's not that big of a problem
with them because they recalculate the quota once in a while anyway. Dict quota
is recalculated only if the quota goes below zero (even this is v1.0.rc30+).

So either you'll have to trust your users not to abuse this problem, or you
could create a nightly cronjob to delete all rows from the SQL quota table to
force a daily recalculation. The recalculation will of course slow down the
server.

This problem will be fixed completely in later Dovecot versions.

Dictionary proxy server
-----------------------

To avoid each process making a new SQL connection, you can make all dictionary
communications go through a dictionary server process which keeps the
connections permanently open.

The dictionary server is referenced with URI 'proxy:<dictionary server socket
path>:<dictionary name>'. The socket path may be left empty if you haven't
changed 'base_dir' setting in 'dovecot.conf'. Otherwise set it to
'<base_dir>/dict-server'. The dictionary names are configured in dovecot.conf.
For example:

---%<-------------------------------------------------------------------------
dict {
  quotadict = mysql:/etc/dovecot-dict-quota.conf
}
---%<-------------------------------------------------------------------------

Example quota plugin configuration for this:

---%<-------------------------------------------------------------------------
plugin {
  quota = dict:storage=10240:messages=1000 proxy::quotadict
}
---%<-------------------------------------------------------------------------

(This file was created from the wiki on 2007-06-15 04:42)