From the Progress in the Face of Acquisition dept.:
...Robin Schumacher, director of product management at Sun's MySQL division, explained that the goal of the new push at MySQL is to have a milestone release every three to six months, the first of those is MySQL 5.4. Today's release is considered by MySQL to be a preview, with the full release set for later this year.

Performance is the key improvement in MySQL 5.4, which comes from a number of innovations in the database. At the top of the list are improvements to the MySQL Optimizer which is the tool that dictates the path the database takes to satisfy queries.

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