I’m running MySQL for most of our DBs right now, and would like to get off the Oracle ship before it takes more of a turn. My understanding is that the transition from MySQL->MariaDB should be trivial, but going the other way is not so easy. Has anyone made this jump yet?
Edit: Bonus points if you have anecdotal information on doing this with Debian/Ubuntu.
I have migrated various servers from MySQL to MariaDB a few weeks ago without any problem.
If you want the full list of what might not be compatible, you can have a look here: http://kb.askmonty.org/en/mariadb-versus-mysql-compatibility.
If you’re upgrading to a higher version of MariaDB than MySQL was, you just have to jsut the mysql_upgrade binary as stated on http://kb.askmonty.org/en/upgrading-to-mariadb-from-mysql.
Moreover, with MariaDB 5.3 (released at the end of July), they now provide a proper repository, so there’s no need to install by hand : http://downloads.askmonty.org/mariadb/repositories/
Check more discussion of this question.