I develop a Rails 3 web app and recently moved from MySQL to MariaDB. Well actually the guys at Rails Machine did the move for me. I don't know what all they did on their end, so can't speak much for the server admin side. We ended up making the switch since I was moving to a high availability setup with multiple DB servers.
On the web app side, I am using the mysql2 gem and made zero changes to my code. Also, I frequently import SQL dumps from MariaDB into my local MySQL development with no problems.
The only issue I had was related to some nasty SQL I had in a select in a finder (yeah I know bad practice). MySQL was returning a 0 while MariaDB returned NULL. Either way, it was my fault for messy code and when I fixed the select, everything was good.
There's one silly difference I noticed. Timestamps in mariadb dumps have their size appended. Mysql doesn't like that, so you need to filter them out. Otherwise pretty much a drop-in.
On the web app side, I am using the mysql2 gem and made zero changes to my code. Also, I frequently import SQL dumps from MariaDB into my local MySQL development with no problems.
The only issue I had was related to some nasty SQL I had in a select in a finder (yeah I know bad practice). MySQL was returning a 0 while MariaDB returned NULL. Either way, it was my fault for messy code and when I fixed the select, everything was good.