We are pleased to announce that you can now upgrade existing MySQL database instances from MySQL 5.1 to MySQL 5.5 using the Major Version Upgrade feature.
MySQL 5.5 offers several feature and performance benefits over MySQL 5.1 for many customers. Some of the improvements include enhanced multi-core scaling, better use of I/O capacity, and enhanced monitoring through the performance schema. Additionally, InnoDB Plugin 1.1 (which is the default storage engine for MySQL 5.5 on Amazon RDS) has several improvements over InnoDB Plugin 1.0 (which is the default storage engine for MySQL 5.1 on Amazon RDS). These improvements include faster recovery, multiple buffer pool instances and asynchronous I/O.
We encourage you to read the release notes, test your applications for compatibility, and upgrade to MySQL 5.5. To upgrade, all you need to do is perform a few clicks on the AWS Management Console. Just select the “Modify” option corresponding to the DB Instance you want to upgrade, choose the latest version of the MySQL 5.5 (you will not be able to upgrade to earlier versions of MySQL 5.5) and proceed with the wizard. The upgrade will be applied either immediately (if you selected the Apply Immediately option) or during your next maintenance window (default). Please note that in either case, your database instance will have an availability impact for a few minutes as the upgrade completes and your database instance is rebooted. Review the Upgrading a DB Instance section of the Amazon RDS User Guide to learn more.