MariaDB vs MySQL for Drupal 6? I am wondering whether it is a good idea to convert a large D6 database of a community site (with 80% read 20% write and about 1300 qps, using MyIsam engine) from Mysql to MariaDB? 

MariaDB seems to be highly desirable:


  MariaDB is a database server that offers drop-in replacement
  functionality for MySQL. MariaDB is built by some of the original
  authors of MySQL, with assistance from the broader community of Free
  and open source software developers. In addition to the core
  functionality of MySQL, MariaDB offers a rich set of feature
  enhancements including alternate storage engines, server
  optimizations, and patches


However I'd like to hear first-hand experiences of fellow drupallers about the expected performance gains. I know that MariaDB uses XtraDB (InnoDB improved) storage engine by default. In fact my site slowed down significantly once I moved the Mysql database to InnoDB engine, so I am a bit unsure about the supposed performance gains.

Also I'd like to know about caveats (possible incompatible modules, etc) of converting to MariaDB. 

Thanks
CAVEAT : This commentary is solely based on MySQL not Drupal.

I have personally worked with Percona Server and MySQL, not with MariaDB as of yet. Percona provides support for MariaDB, Drizzle, Amazon RDS, and other MySQL products.

I learned at Percona Live NYC that Percona gets the latest version of MySQL and injects 30,000 lines of C/C++ that is unique to its Performance Enhancements. MySQL (eh, Oracle) tries to keep up with its own enhancements of InnoDB.

Unless your Drupal website is very heavily trafficked, there is no decent performance difference you can feel or see. However, if you do have high traffic and you want to compare MySQL, Percona, and MariaDB, I have posted an article in the DBA StackExchange on how to go about doing this.