The recently released MySQL 5.6 gets a lot of attention, but for those who are still on 5.5 there is also good news: There are two new features in 5.5.
The first feature is that there are more INFORMATION_SCHEMA tables for InnoDB. This means that it's possible to 'see' what's in the buffer pool. It also makes it possible to get more information about the LRU list.
From the 5.5.28 changelog:
InnoDB: Certain information_schema tables originally introduced in MySQL 5.6 are now also available in MySQL 5.5 and MySQL 5.1: INNODB_BUFFER_PAGE, INNODB_BUFFER_PAGE_LRU, and INNODB_BUFFER_POOL_STATS. (Bug #13113026)
This is in the "Bugs Fixed" section instead of the "Functionality Added or Changed" section, which is a bit weird in my opinion.
The second feature is a variable which makes it possible to get more information about the deadlocks.
From the 5.5.30 changelog:
InnoDB: The innodb_print_all_deadlocks configuration option from MySQL 5.6 was backported to MySQL 5.5. This option records each deadlock condition in the MySQL error log, allowing easier troubleshooting if frequent deadlocks point to application coding issues. (Bug #14515889)
So updating to the latest 5.5 (or even 5.1) is not only good for security, stability and performance but it also brings some nice new features.