MySQL Native Driver Plugin API
PHP Manual

The mysqlnd plugin API

The following is a list of functions provided in the mysqlnd plugin API:

There is no formal definition of what a plugin is and how a plugin mechanism works.

Components often found in plugins mechanisms are:

The mysqlnd plugin concept employs these features, and additionally enjoys an open architecture.

No Restrictions

A plugin has full access to the inner workings of mysqlnd. There are no security limits or restrictions. Everything can be overwritten to implement friendly or hostile algorithms. It is recommended you only deploy plugins from a trusted source.

As discussed previously, plugins can use pointers freely. These pointers are not restricted in any way, and can point into another plugin's data. Simple offset arithmetic can be used to read another plugin's data.

It is recommended that you write cooperative plugins, and that you always call the parent method. The plugins should always cooperate with mysqlnd itself.

Issues: an example of chaining and cooperation
Extension mysqlnd.query() pointer call stack if calling parent
ext/mysqlnd mysqlnd.query() mysqlnd.query
ext/mysqlnd_cache mysqlnd_cache.query()
  1. mysqlnd_cache.query()

  2. mysqlnd.query

ext/mysqlnd_monitor mysqlnd_monitor.query()
  1. mysqlnd_monitor.query()

  2. mysqlnd_cache.query()

  3. mysqlnd.query

In this scenario, a cache (ext/mysqlnd_cache) and a monitor (ext/mysqlnd_monitor) plugin are loaded. Both subclass Connection::query(). Plugin registration happens at MINIT using the logic shown previously. PHP calls extensions in alphabetical order by default. Plugins are not aware of each other and do not set extension dependencies.

By default the plugins call the parent implementation of the query method in their derived version of the method.

PHP Extension Recap

This is a recap of what happens when using an example plugin, ext/mysqlnd_plugin, which exposes the mysqlnd C plugin API to PHP:

MySQL Native Driver Plugin API
PHP Manual