some times it could be desirable to close DB connections and reopen them again. In order to achieve this moodle_database objects should implement one disconnect() method, simply closing the connection (but leaving the moodle_database object created).

Also, perhaps some is_connected() or so should be able to return true/false and all moodle_database functions handling DB info should start with one:

if (!is_connected) {
    return false;
}

Ciao :-)