Monty Widenius' MariaDB fork of MySQL took another step in development today.  MariaDB 5.1, which is based on MySQL 5.1.41 is now available in release candidate form for download and testing.  Widenius, a founder of MySQL, said the release had a four month beta cycle and the development team is confident that the RC is very stable.  The 5.1 release adds more databases and it includes 'pool of threads' and 'table elimination' features.

According to the project wiki, the goal of Maria is to make a crash-safe alternative to MyISAM so that when mysqld restarts after a crash, Maria recovers all tables to the last state at the start of a statement or at the start of a LOCK TABLES.  Maria isn't transactional yet, but it's long-term goal is to add that support and become the default transactional and non-transactional storage engine for MySQL.

In MariaDB 5.1.41, XtraDB now replaces InnoDB.  This will give users most of the performance gains coming in MySQL 5.4 today.  Some benchmarks from the MySQL Performance Blog show XtraDB outperforming InnoDB by a significant margin.  XtraDB also has Google and Percona enhancements built-in so there's no need to load it as a plugin.

The PrimeBase XT transactional engine is another new storage engine included in MariaDB 5.1.  It has a unique "write-once" update strategy and MVCC (multi-version concurrency control) to provide optimal performance over a wide range of tasks.  Finally, replacing the old, unmaintained Federated engine from Sun is the FederatedX storage engine.

The pool of threads feature, based on code from the canceled MySQL 6.0 release, has been added to MariaDB.  Pool of threads lets users designate a limited set of threads to handle all queries and allows more than the usual 'one-thread-per-connection'.  It's very helpful if there are a lot of database connections being used or there are a lot of short-lived queries.  Table elimination is a new feature that optimizes certain types of joins.  The basic idea behind table elimination is that sometimes it is possible to resolve a query without even accessing some of the tables that the query refers to.

MariaDB 5.1.41 has several patches from the MySQL community including Microslow and Microsec from Percona.  MariaDB 5.1 also added the following extensions:

• MariaDB can handle up to 32 key segments per key (up from 16)
• Added a new handler function: prepare_index_scan() that is called before a key scan is done.
• Added --abort-source-on-error to the mysql client.

Finally, speed improvements and bug fixes were added to MariaDB, and now the development team is looking for feedback before the final release.