MySQL 5.5 Milestone 2 improves replication and stored procedures
The MySQL developers have released milestone 2 of MySQL 5.5, on the path to a general release in mid-2010. The new milestone release incorporates semi-synchronous replication in MySQL 5.5 based on patches to InnoDB developed by Google. This is designed to ensure that when a change is committed in the master database, at least one slave has confirmed that the data has arrived and been buffered before the commit is complete.
Developers of SQL procedures will find the addition of SQL standard exception handling, SIGNAL and RESIGNAL, should give them the ability to make stored procedures more robust and easier to debug.
Partitioning, which allows data within a table to be distributed over a cluster, has also been enhanced. An improved partitioning syntax lifts previous restrictions of only partitioning based on one INTEGER column, and allows for data to be partitioned based on multiple columns with dates, datetime, strings and integers.
An overview of the changes in MySQL is available online along with the change notes. MySQL 5.5 Milestone 2 is described as "not production ready" but "suitable for testing and feedback". It can be downloaded from the MySQL download site.