PECL/mysqlnd_mux adds multiplexing to all PHP MySQL APIs (mysql, mysqli, PDO_MySQL) compiled to use mysqlnd. Connection multiplexing refers to sharing one MySQL connection among multiple user connection handles, among multiple clients. Multiplexing does reduce client-side connection overhead and minimizes the total number of concurrently open connections. The latter lowers the MySQL server load. As a highly specific optimization it has not only strong but also weak sides. See, what this free plugin has to offer in prototype stage. And, how does it compare to other techniques such as pooling or persistent connections - what to use when tuning PHP MySQL to the extreme.