The main goal of migrating to MariaDB is not performance driven. More so,
I think it's in WMF's and the open source communities interest to coalesce
around the MariaDB Foundation as the best route to ensuring a truly open
and well supported future for mysql derived database technology.
Performance gains along the way are icing on the cake.
If you want to see a bunch of other cool public Ganglia instances you can do a search something like:
Also, despite the switch on db59 happening a few days ago, there doesn't seem to be a significant change in overall CPU usage: http://ganglia.wikimedia.org/latest/graph.php?r=month&z=...
Also, most MediaWiki installs use plugins, and those plugins often create their own database tables. So RDBMS is pretty much baked into the MediaWiki culture.
However, MediaWiki is fairly well abstracted from any particular RDBMS implementation. Everything from creating tables to making a join is done through an API.
The difference today is that open source projects have made document stores and 'nosql' technologies more accessible.
MariaDB has XtraDB, which is a drop-in replacement for InnoDB; I'm not sure if it's encumbered or not, given it's Percona's fork of InnoDB.
(Does anyone have any experience using XtraDB that they can relate?)
This website has some benchmarks to prove it: http://vbtechsupport.com/606/ http://vbtechsupport.com/657/2/
But there are other reasons to look at mariadb/percona.
MediaWiki, the open source software that Wikipedia uses, now officially supports MariaDB.
I'm not a ganglia wizard - maybe this comes close? Although it's just all selects. I think.
You might try asking on wikitech-l, the same mailing list that the original post comes from.