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
 * PostgreSQL
 * Flat file

The quota root format is:

---%<-------------------------------------------------------------------------
quota = dict:<quota root name>:<username>[:<option>[...]]:<dictionary URI>
---%<-------------------------------------------------------------------------

If /username/ is left empty, the logged in username is used (this is typically
what you want). Another useful username is '%d' for supporting domain-wide
quotas.

The supported options are:

 * noenforcing: Don't enforce quota limits, only track them.
 * ignoreunlimited: If user has unlimited quota, don't track it.
 * ns=<prefix>: This quota root is tracked only for the given namespace.

NOTE: The dictionary stores only the current quota usage. The quota limits are
still configured in userdb the same way as with other quota backends.

Examples
--------

---%<-------------------------------------------------------------------------
plugin {
  # SQL backend:
  quota = dict:User quota::proxy::quota
  # file backend:
  quota = dict:User quota::file:%h/Maildir/dovecot-quota

  quota_rule = *:storage=10M:messages=1000
}
dict {
  quota = mysql:/etc/dovecot/dovecot-dict-sql.conf.ext
}
---%<-------------------------------------------------------------------------

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.ext':

---%<-------------------------------------------------------------------------
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)
);
---%<-------------------------------------------------------------------------

MySQL uses the following queries to update the quota. You need suitable
privileges.

---%<-------------------------------------------------------------------------
INSERT INTO table (bytes,username) VALUES ('112497180','foo@spam.dom') ON
DUPLICATE KEY UPDATE bytes='112497180';
INSERT INTO table (messages,username) VALUES ('1743','foo@spam.dom') ON
DUPLICATE KEY UPDATE messages='1743';
UPDATE table SET bytes=bytes-14433,messages=messages-2 WHERE username =
'foo@spam.dom';
---%<-------------------------------------------------------------------------

If you're using PostgreSQL, you'll need a trigger:

---%<-------------------------------------------------------------------------
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();
---%<-------------------------------------------------------------------------

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/dovecot-dict-sql.conf.ext
  expire = mysql:/etc/dovecot/dovecot-dict-sql.conf.ext
}
---%<-------------------------------------------------------------------------

See <Dict.txt> for more information, especially about permission issues.

(This file was created from the wiki on 2012-07-03 04:42)
