The mysqlnd user handler plugin can be understood as a client-side proxy for all PHP MySQL extensions (mysqli, mysql, PDO_MYSQL), if they are compiled to use the mysqlnd library. The extensions use the mysqlnd library internally, at the C level, to communicate with the MySQL server. PECL/mysqlnd_uh allows it to hook many mysqlnd calls. Therefore, most activities of the PHP MySQL extensions can be monitored. Because monitoring happens at the level of the library, at a layer below the application, it is possible to monitor applications without changing them. On the C level, the mysqlnd library is structured in modules or classes. The extension hooks almost all methods of the mysqlnd internal connection class and exposes them through the user space class MysqlndUhConnection. Some few methods of the mysqlnd internal statement class are made available to the PHP user with the class MysqlndUhPreparedStatement. By subclassing the classes MysqlndUhConnection and MysqlndUhPreparedStatement users get access to mysqlnd internal function calls. The internal mysqlnd function calls are not designed to be exposed to the PHP user. Manipulating their activities may cause PHP to crash or leak memory. Often, this is not considered a bug. Please, keep in mind that you are accessing C library functions through PHP which are expected to take certain actions, which you may not be able to emulate in user space. Therefore, it is strongly recommended to always call the parent method implementation when subclassing MysqlndUhConnection or MysqlndUhPreparedStatement. To prevent the worst case, the extension performs some sanity checks. Please, see also the Mysqlnd_uh &ConfigureOptions;.

The plugin is implemented as a PHP extension. See the installation instructions to install the PECL/mysqlnd_uh extension. Then, load the extension into PHP and activate the plugin in the PHP configuration file using the PHP configuration directive named mysqlnd_uh.enable. The below example shows the default settings of the extension.

This describes the background and inner workings of the mysqlnd_uh extension. Two classes are provided by the extension: MysqlndUhConnection and MysqlndUhPreparedStatement. MysqlndUhConnection lets you access almost all methods of the mysqlnd internal connection class. The latter exposes some selected methods of the mysqlnd internal statement class. For example, MysqlndUhConnection::connect maps to the mysqlnd library C function mysqlnd_conn__connect. As a mysqlnd plugin, the PECL/mysqlnd_uh extension replaces mysqlnd library C functions with its own functions. Whenever a PHP MySQL extension compiled to use mysqlnd calls a mysqlnd function, the functions installed by the plugin are executed instead of the original mysqlnd ones. For example, mysqli_connect invokes mysqlnd_conn__connect, so the connect function installed by PECL/mysqlnd_uh will be called. The functions installed by PECL/mysqlnd_uh are the methods of the built-in classes. The built-in PHP classes and their methods do nothing but call their mysqlnd C library counterparts, to behave exactly like the original mysqlnd function they replace. The code below illustrates in pseudo-code what the extension does. The build-in classes behave like a transparent proxy. It is possible for you to replace the proxy with your own. This is done by subclassing MysqlndUhConnection or MysqlndUhPreparedStatement to extend the functionality of the proxy, followed by registering a new proxy object. Proxy objects are installed by mysqlnd_uh_set_connection_proxy and mysqlnd_uh_set_statement_proxy. ]]> &example.outputs; NULL, 1 => 'localhost', 2 => 'root', 3 => '', 4 => 'test', 5 => 3306, 6 => NULL, 7 => 131072, )) proxy::connect returns true ]]>

The extension provides two built-in classes: MysqlndUhConnection and MysqlndUhPreparedStatement. The classes are used for hooking mysqlnd library calls. Their methods correspond to mysqlnd internal functions. By default they act like a transparent proxy and do nothing but call their mysqlnd counterparts. By subclassing the classes you can install your own proxy to monitor mysqlnd. See also the How it works guide to learn about the inner workings of this extension. Connection proxies are objects of the type MysqlndUhConnection. Connection proxy objects are installed by mysqlnd_uh_set_connection_proxy. If you install the built-in class MysqlndUhConnection as a proxy, nothing happens. It behaves like a transparent proxy. ]]> The PHP_INI_SYSTEM configuration setting mysqlnd_uh.enable controls whether a proxy may be set. If disabled, the extension will throw errors of type E_WARNING ]]> &example.outputs; To monitor mysqlnd, you have to write your own proxy object subclassing MysqlndUhConnection. Please, see the function reference for a the list of methods that can be subclassed. Alternatively, you can use reflection to inspect the built-in MysqlndUhConnection. Create a new class proxy. Derive it from the built-in class MysqlndUhConnection. Replace the MysqlndUhConnection::connect. method. Print out the host parameter value passed to the method. Make sure that you call the parent implementation of the connect method. Failing to do so may give unexpected and undesired results, including memory leaks and crashes. Register your proxy and open three connections using the PHP MySQL extensions mysqli, mysql, PDO_MYSQL. If the extensions have been compiled to use the mysqlnd library, the proxy::connect method will be called three times, once for each connection opened. ]]> &example.outputs; The use of prepared statement proxies follows the same pattern: create a proxy object of the type MysqlndUhPreparedStatement and install the proxy using mysqlnd_uh_set_statement_proxy. prepare("SELECT 'mysqlnd hacking made easy' AS _msg FROM DUAL"); ?> ]]> &example.outputs;

Basic monitoring of a query statement is easy with PECL/mysqlnd_uh. Combined with debug_print_backtrace it can become a powerful tool, for example, to find the origin of certain statement. This may be desired when searching for slow queries but also after database refactoring to find code still accessing deprecated databases or tables. The latter may be a complicated matter to do otherwise, especially if the application uses auto-generated queries. query("SELECT 1 AS _one FROM DUAL")->fetchAll(PDO::FETCH_ASSOC)); $mysqli = new mysqli("localhost", "root", "", "test"); $mysqli->prepare("SELECT 1 AS _two FROM DUAL"); ?> ]]> &example.outputs; query(Resource id #19, SELECT 1 AS _one FROM DUAL) #1 PDO->query(SELECT 1 AS _one FROM DUAL) called at [example.php:19] array(1) { [0]=> array(1) { ["_one"]=> string(1) "1" } } #0 stmt_proxy->prepare(Resource id #753, SELECT 1 AS _two FROM DUAL) #1 mysqli->prepare(SELECT 1 AS _two FROM DUAL) called at [example.php:22] ]]> For basic query monitoring you should install a connection and a prepared statement proxy. The connection proxy should subclass MysqlndUhConnection::query. All database queries not using native prepared statements will call this method. In the example the query function is invoked by a PDO call. By default, PDO_MySQL is using prepared statement emulation. All native prepared statements are prepared with the prepare method of mysqlnd exported through MysqlndUhPreparedStatement::prepare. Subclass MysqlndUhPreparedStatement and overwrite prepare for native prepared statement monitoring.