Compile or configure the PHP MySQL extension (mysqli, PDO_MYSQL, mysql) that you plan to use with support for the mysqlnd library. PECL/mysqlnd_qc is a plugin for the mysqlnd library. To use the plugin with any of the existing PHP MySQL extensions (APIs), the extension has to use the mysqlnd library.
Then, load the extension into PHP and activate the plugin in the PHP configuration file using the PHP configuration directive named mysqlnd_qc.enable_qc.
Example #1 Enabling the plugin (php.ini)