Ulf Wendel has a new post that compares the performance of a classic method for using the mysqlnd plugin in MySQL replication to mysqlnd_ms, the replication and load balancing plugin for the mysqlnd driver (that works with the mysql and mysqli functionality and is, as of this beta of PHP, the default driver for MySQL connections).
Recently I was asked if PECL/mysqlnd_ms should be used to add MySQL replication support to a yet to be developed PHP application. The mysqlnd plugin, which supports all PHP MySQL extensions (PDO, mysqli, mysql), stood up against a classical, simple, proven and fast approach: one connection for reads, one connection for writes. Let's compare. This is a bit of an unfair challenge, because PECL/mysqlnd_ms was designed as a drop-in for existing applications, not optimized for those starting from scratch, *yell*... The plugin stands up quite well, anyway!
He starts with a look at the "classical pattern" of using a factory or singleton to make a database object instance that gives back different connections for reads versus writes (slave vs master). The mysqlnd_ms plugin allows you to define configuration settings to tell the queries to automatically go to certain places for different actions. For example, you could use "master_on_write" to tell it to use a master node if you're doing an INSERT or UPDATE versus a SELECT. He also shows a more complex example using a SQL hint and one issue that might come from the "human element" - not paying attention to database character sets.