MySQL has released its second milestone of the new series, inaugurated this year with MySQL 5.4.
The new installment, MySQL 5.5-m2, has several new features, of which the most notables ones are semi-synchronous replication, exception handling through in stored routines through SIGNAL and RESIGNAL, and partitioning enhancements.
A quick overview of partitioning and semi-synchronous replication is available in this blog. Hours after the release, Roland Bouman published a very charming example of how useful the new SIGNAL feature can be.
This release shows that MySQL is moving forward in the path of its new development cycle, leaving behind its previous inflexible model that was stalling innovation and contribution. With this agile cycle, mature features are added more dynamically, while the ones in need of more development are sent to the next milestone, without side effects.