More interesting (to me, at least) than the query analyzer and debug tracing (to a proprietary tool which costs money) is the mysqlnd_ms plugin, that can seems

More interesting (to me, at least) than the query analyzer and debug tracing (to a proprietary tool which costs money) is the mysqlnd_ms plugin, that can seems to be able to gracefully handle switching between multiple mysql connections to simplify query routing for master/slave or load balancing setups. Handling that on the driver level (I'm already a big fan of mysqlnd async) could help you ease your code into a replicated environment.