# Introduction

The mysqlnd multiplexing plugin (`mysqlnd_mux`) multiplexes MySQL connections established by all PHP MySQL extensions that use the MySQL native driver (mysqlnd) for PHP.

The MySQL native driver for PHP features an internal C API for plugins, such as the connection multiplexing plugin, which can extend the functionality of mysqlnd. See the mysqlnd for additional details about its benefits over the MySQL Client Library libmysqlclient.

Mysqlnd plugins like `mysqlnd_mux` operate, for the most part, transparently from a user perspective. The connection multiplexing plugin supports all PHP applications, and all MySQL PHP extensions. It does not change existing APIs. Therefore, it can easily be used with existing PHP applications.

> Note:

> This is a proof-of-concept. All features are at an early stage. Not all kinds of queries are handled by the plugin yet. Thus, it cannot be used in a drop-in fashion at the moment.

> Please, do not use this version in production environments.

## Key Features

The key features of mysqlnd_mux are as follows:

- Transparent and therefore easy to use:

  - Supports all of the PHP MySQL extensions.

  - Little to no application changes are required, dependent on the required usage scenario.

- Reduces server load and connection establishment latency:

  - Opens less connections to the MySQL server.

  - Less connections to MySQL mean less work for the MySQL server. In a client-server environment scaling the server is often more difficult than scaling the client. Multiplexing helps with horizontal scale-out (scale-by-client).

  - Pooling saves connection time.

  - Multiplexed connection: multiple user handles share the same network connection. Once opened, a network connection is cached and shared among multiple user handles. There is a 1:n relationship between internal network connection and user connection handles.

  - Persistent connection: a network connection is kept open at the end of the web request, if the PHP deployment model allows. Thus, subsequently web requests can reuse a previously opened connection. Like other resources, network connections are bound to the scope of a process. Thus, they can be reused for all web requests served by a process.

## Limitations

The proof-of-concept does not support unbuffered queries, prepared statements, and asynchronous queries.

The connection pool is using a combination of the transport method and hostname as keys. As a consequence, two connections to the same host using the same transport method (TCP/IP, Unix socket, Windows named pipe) will be linked to the same pooled connection even if username and password differ. Be aware of the possible security implications.

The proof-of-concept is transaction agnostic. It does not know about SQL transactions.

> Note:

> Applications must be aware of the consequences of connection sharing connections.

## About the name mysqlnd_mux

The shortcut `mysqlnd_mux` stands for `mysqlnd connection multiplexing plugin`.