

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
===================


With Dovecot v1.1 quota is tracked accurately. With v1.0 you may have a problem: 
If two IMAP clients do an expunge at the same time, the quota is reduced twice as much. Maildir++ backend also has the same problem, but it's not that big of a problem with it because it recalculates the quota once in a while anyway. Dict quota is recalculated only if the quota goes below zero (v1.0.rc30+ only). 
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. 


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 2007-12-11 04:42)
