protected function conn_create($dsn)
    {
        // Get database specific connection options
        $dsn_options = $this->dsn_options($dsn);

        $function = $this->db_pconn ? 'oci_pconnect' : 'oci_connect';

        if (!function_exists($function)) {
            $this->db_error     = true;
            $this->db_error_msg = 'OCI8 extension not loaded. See http://php.net/manual/en/book.oci8.php';

            rcube::raise_error(array('code' => 500, 'type' => 'db',
                'line' => __LINE__, 'file' => __FILE__,
                'message' => $this->db_error_msg), true, false);

            return;
        }

        // connect
        $dbh = @$function($dsn['username'], $dsn['password'], $dsn_options['database'], $dsn_options['charset']);

        if (!$dbh) {
            $error              = oci_error();
            $this->db_error     = true;
            $this->db_error_msg = $error['message'];

            rcube::raise_error(array('code' => 500, 'type' => 'db',
                'line' => __LINE__, 'file' => __FILE__,
                'message' => $this->db_error_msg), true, false);

            return;
        }

        // configure session
        $this->conn_configure($dsn, $dbh);

        return $dbh;
    }