The problem is valid for 5.5 and needs to be fixed.

# rpm -qa | grep Percona
Percona-Server-shared-compat-5.5.35-rel33.0.611.rhel6.x86_64
Percona-Server-client-55-5.5.39-rel36.0.el6.x86_64
Percona-Server-server-55-5.5.39-rel36.0.el6.x86_64
Percona-Server-shared-55-5.5.39-rel36.0.el6.x86_64
Percona-Server-devel-55-5.5.39-rel36.0.el6.x86_64


Here is an excerpt from the yum update output

Downloading Packages:
(1/4): Percona-Server-client-55-5.5.40-rel36.1.el6.x86_6 | 5.9 MB     00:00     
(2/4): Percona-Server-devel-55-5.5.40-rel36.1.el6.x86_64 | 946 kB     00:00     
(3/4): Percona-Server-server-55-5.5.40-rel36.1.el6.x86_6 |  15 MB     00:00     
(4/4): Percona-Server-shared-55-5.5.40-rel36.1.el6.x86_6 | 648 kB     00:00     
--------------------------------------------------------------------------------
Total                                            46 MB/s |  23 MB     00:00     
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Updating   : Percona-Server-shared-55-5.5.40-rel36.1.el6.x86_64           1/8 
  Updating   : Percona-Server-client-55-5.5.40-rel36.1.el6.x86_64           2/8 
  Updating   : Percona-Server-server-55-5.5.40-rel36.1.el6.x86_64           3/8 
ls: cannot access /opt/mysql/dbdata1/reference-p0/*.err: No such file or directory
ls: cannot access /opt/mysql/dbdata1/reference-p0/*.err: No such file or directory
Giving mysqld 5 seconds to exit nicely
Percona Server is distributed with several useful UDF (User Defined Function) from Percona Toolkit.
Run the following commands to create these functions:
mysql -e "CREATE FUNCTION fnv1a_64 RETURNS INTEGER SONAME 'libfnv1a_udf.so'"
mysql -e "CREATE FUNCTION fnv_64 RETURNS INTEGER SONAME 'libfnv_udf.so'"
mysql -e "CREATE FUNCTION murmur_hash RETURNS INTEGER SONAME 'libmurmur_udf.so'"
See http://www.percona.com/doc/percona-server/5.5/management/udf_percona_toolkit.html for more details
  Updating   : Percona-Server-devel-55-5.5.40-rel36.1.el6.x86_64            4/8 
  Cleanup    : Percona-Server-devel-55-5.5.39-rel36.0.el6.x86_64            5/8 
  Cleanup    : Percona-Server-server-55-5.5.39-rel36.0.el6.x86_64           6/8 
  Cleanup    : Percona-Server-client-55-5.5.39-rel36.0.el6.x86_64           7/8 
  Cleanup    : Percona-Server-shared-55-5.5.39-rel36.0.el6.x86_64           8/8 
  Verifying  : Percona-Server-devel-55-5.5.40-rel36.1.el6.x86_64            1/8 
  Verifying  : Percona-Server-server-55-5.5.40-rel36.1.el6.x86_64           2/8 
  Verifying  : Percona-Server-shared-55-5.5.40-rel36.1.el6.x86_64           3/8 
  Verifying  : Percona-Server-client-55-5.5.40-rel36.1.el6.x86_64           4/8 
  Verifying  : Percona-Server-client-55-5.5.39-rel36.0.el6.x86_64           5/8 
  Verifying  : Percona-Server-devel-55-5.5.39-rel36.0.el6.x86_64            6/8 
  Verifying  : Percona-Server-shared-55-5.5.39-rel36.0.el6.x86_64           7/8 
  Verifying  : Percona-Server-server-55-5.5.39-rel36.0.el6.x86_64           8/8 

Updated:
  Percona-Server-client-55.x86_64 0:5.5.40-rel36.1.el6                          
  Percona-Server-devel-55.x86_64 0:5.5.40-rel36.1.el6                           
  Percona-Server-server-55.x86_64 0:5.5.40-rel36.1.el6                          
  Percona-Server-shared-55.x86_64 0:5.5.40-rel36.1.el6                          

Complete!



# mysql
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/opt/mysql/dbprod/reference-p0.sock' (2)
[root@mirror ~]# service mysql restart
MySQL (Percona Server) PID file could not be found!        [FAILED]
Starting MySQL (Percona Server)...........                 [  OK  ]