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

The /dictionary/ quota backend supports both *storage* and *messages* quota
limits. The current quota is kept in a dictionary. The available dictionaries
are:

 * MySQL (v1.0+)
 * PostgreSQL (v1.1.2+)
 * Flat file (v1.2.alpha3+)

The plugin parameter format is:

---%<-------------------------------------------------------------------------
# v1.0:
quota = dict:<quota limits> <dictionary URI>
# v1.1+:
quota = dict:<quota root name>:<user name>:<dictionary URI>
---%<-------------------------------------------------------------------------

If user name is left empty, the logged in username is used (this is probably
what you want).

v1.0 & v1.1
-----------

Example:

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

plugin {
  # v1.0: 10MB and 1000 messages quota limit
  quota = dict:storage=10240:messages=1000 proxy::quotadict

  # v1.1 + SQL:
  quota = dict:user::proxy::quotadict
  quota_rule = *:storage=10M:messages=1000
}
---%<-------------------------------------------------------------------------

The above example uses dictionary proxy process (see below), because SQL
libraries aren't linked to all Dovecot binaries.

Example 'dovecot-dict-quota.conf':

---%<-------------------------------------------------------------------------
# v1.0 and v1.1 only - v1.2 has different configuration
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)
);
---%<-------------------------------------------------------------------------

v1.2+
-----

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

plugin {
  # v1.2 + SQL:
  quota = dict:user::proxy::quotadict
  # v1.2 + file:
  quota = dict:user::file:%h/Maildir/dovecot-quota

  quota_rule = *:storage=10M:messages=1000
}
---%<-------------------------------------------------------------------------

The above SQL example uses dictionary proxy process (see below), because SQL
libraries aren't linked to all Dovecot binaries. The file example accesses the
file directly.

Example 'dovecot-dict-sql.conf':

---%<-------------------------------------------------------------------------
# v1.2+ only:
connect = host=localhost dbname=mails user=sqluser password=sqlpass
map {
  pattern = priv/quota/storage
  table = quota
  username_field = username
  value_field = bytes
}
map {
  pattern = priv/quota/messages
  table = quota
  username_field = username
  value_field = messages
}
---%<-------------------------------------------------------------------------

Create the table like this:

---%<-------------------------------------------------------------------------
CREATE TABLE quota (
  username varchar(100) not null,
  bytes bigint not null default 0,
  messages integer not null default 0,
  primary key (username)
);
---%<-------------------------------------------------------------------------

If you're using PostgreSQL, you'll need a trigger (v1.2.beta1+):

---%<-------------------------------------------------------------------------
CREATE OR REPLACE FUNCTION merge_quota() RETURNS TRIGGER AS $$
BEGIN
  IF NEW.messages < 0 OR NEW.messages IS NULL THEN
    -- ugly kludge: we came here from this function, really do try to insert
    IF NEW.messages IS NULL THEN
      NEW.messages = 0;
    ELSE
      NEW.messages = -NEW.messages;
    END IF;
    return NEW;
  END IF;

  LOOP
    UPDATE quota SET bytes = bytes + NEW.bytes,
      messages = messages + NEW.messages
      WHERE username = NEW.username;
    IF found THEN
      RETURN NULL;
    END IF;

    BEGIN
      IF NEW.messages = 0 THEN
        INSERT INTO quota (bytes, messages, username)
          VALUES (NEW.bytes, NULL, NEW.username);
      ELSE
        INSERT INTO quota (bytes, messages, username)
          VALUES (NEW.bytes, -NEW.messages, NEW.username);
      END IF;
      return NULL;
    EXCEPTION WHEN unique_violation THEN
      -- someone just inserted the record, update it
    END;
  END LOOP;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER mergequota BEFORE INSERT ON quota
   FOR EACH ROW EXECUTE PROCEDURE merge_quota();
---%<-------------------------------------------------------------------------

v1.0 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 {
  quota = mysql:/etc/dovecot-dict-quota.conf
  expire = mysql:/etc/dovecot-dict-expire.conf
}
---%<-------------------------------------------------------------------------

(This file was created from the wiki on 2009-03-02 04:42)
