Based on MySQL 5.5.33, including all the bug fixes in it, Percona Server 5.5.33-31.1 is now the current stable release in the 5.5 series. All of Percona‘s software is open-source and free, all the details of the release can be found in the 5.5.33-31.1 milestone at Launchpad.
The buffer pool mutex split patch implemented in Percona Server could cause a race condition, involving a dirty compressed page block for which there is an uncompressed page image in the buffer pool, that could lead to a server crash. Bug fixed #1086680.
Percona Server shared-compat package was being built with the 5.1.66 version of the client, which didn’t work with OpenSSL. Fixed by building the shared-compat package with a more recent version. Bug fixed #1201393.
Percona Server used to acquire the buffer pool LRU list mutex in the I/O completion routine for the compressed page flush list flushes where it was not necessary. Bug fixed #1181269.