維基百科的 mailing list 上丟出的消息，英文版 Wikipedia 資料庫的 slave server 目前已經在 MariaDB 5.5 上了：「mariadb 5.5 in production for english wikipedia」。
之前跑的版本是 MySQL 5.1 + Facebook patchset 版本，整體大約快了 8%：
Taking the times of 100% of all queries over regular sample windows, the average query time across all enwiki slave queries is about 8% faster with MariaDB vs. our production build of 5.1-fb. Some queries types are 10-15% faster, some are 3% slower, and nothing looks aberrant beyond those bounds. Overall throughput as measured by qps has generally been improved by 2-10%. I wouldn't draw any conclusions from this data yet, more is needed to filter out noise, but it's positive.
MariaDB has some nice performance improvements that our workload doesn't really hit (better query optimization and index usage during joins, much better sub query support) but there are also some things, such as full utilization of the primary key embedded on the right of every secondary index that we can take advantage of (and improve our schema around) once prod is fully upgraded, hopefully over the next 1-2 months.
效能不是最主要考量，而是政治面的原因，官方說法是支持 open source 社群：(沒有講的就是「我們對 Oracle 不怎麼信任...」)
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.
另外參考：「on wikipedia and mariadb」。