For developers: 1/ try functional DB tests for all 4 drivers (except mysqli) 2/ try to connect to external database and fetch list tables: Try to connect to an external DB with empty prefix: $prefix = '';   if (!$handler = moodle_database::get_driver_instance($type, $library, true)) { throw new dml_exception('dbdriverproblem', "Unknown driver $library/$db_record->type"); } try { $handler->connect($host, $username, $password, $name, $prefix, $options); } catch (moodle_exception $e) { die(); }   print_r($handler->get_tables(false));