A comparison of mysqlnd plugins with MySQL
Proxy

Mysqlnd plugins and MySQL Proxy are
different technologies using different approaches. Both are valid
tools for solving a variety of common tasks such as load balancing,
monitoring, and performance enhancements. An important difference
is that MySQL Proxy works with all MySQL clients, whereas
mysqlnd plugins are specific to PHP applications.

As a PHP Extension, a mysqlnd plugin gets
installed on the PHP application server, along with the rest of
PHP. MySQL Proxy can either be run on the PHP application server or
can be installed on a dedicated machine to handle multiple PHP
application servers.

Deploying MySQL Proxy on the application server has
two advantages:

1. No single point of failure

2. Easy to scale out (horizontal scale out, scale by
   client)

MySQL Proxy (and mysqlnd plugins) can
solve problems easily which otherwise would have required changes
to existing applications.

However, MySQL Proxy does have some
disadvantages:

• MySQL Proxy is a new component and technology to
  master and deploy.

• MySQL Proxy requires knowledge of the Lua scripting
  language.

MySQL Proxy can be customized with C and Lua
programming. Lua is the preferred scripting language of MySQL
Proxy. For most PHP experts Lua is a new language to learn. A
mysqlnd plugin can be written in C. It is also possible to
write plugins in PHP using » PECL/mysqlnd_uh.

MySQL Proxy runs as a daemon – a background
process. MySQL Proxy can recall earlier decisions, as all state can
be retained. However, a mysqlnd plugin is bound to the
request-based lifecycle of PHP. MySQL Proxy can also share one-time
computed results among multiple application servers. A
mysqlnd plugin would need to store data in a persistent
medium to be able to do this. Another daemon would need to be used
for this purpose, such as Memcache. This gives MySQL Proxy an
advantage in this case.

MySQL Proxy works on top of the wire protocol. With
MySQL Proxy you have to parse and reverse engineer the MySQL Client
Server Protocol. Actions are limited to those that can be achieved
by manipulating the communication protocol. If the wire protocol
changes (which happens very rarely) MySQL Proxy scripts would need
to be changed as well.

Mysqlnd plugins work on top of the C API,
which mirrors the libmysqlclient client and Connector/C
APIs. This C API is basically a wrapper around the MySQL Client
Server protocol, or wire protocol, as it is sometimes called. You
can intercept all C API calls. PHP makes use of the C API,
therefore you can hook all PHP calls, without the need to program
at the level of the wire protocol.

Mysqlnd implements the wire protocol.
Plugins can therefore parse, reverse engineer, manipulate and even
replace the communication protocol. However, this is usually not
required.

As plugins allow you to create implementations that
use two levels (C API and wire protocol), they have greater
flexibility than MySQL Proxy. If a mysqlnd plugin is
implemented using the C API, any subsequent changes to the wire
protocol do not require changes to the plugin itself.