Released just a few days after the release of Redhat Enterprise Linux 5.9, the Oracle Linux version 5.9 is the latest operating system from the database company that provides zero-downtime patching; is optimized for Oracle hardware and software; and is enterprise ready.
Unbreakable Enterprise Kernel 2 is based on Linux 2.6.39-300 kernel. Some of the major improvements according to Oracle in the kernel are performance and scalability improvements, virtualization improvements, Transparent Huge Pages and Memory compaction and OCFS2 improvements. The new Unbreakable kernel comes with Btrfs file-system and newer device drivers.
For more details about this release head onto Oracle blogs.