I have had no luck getting MySQL 5.5 to be as fast as 5.1 or MariaDB on the exact same hardware/database/environment under Windows server 2003R2 or 2008R2.
My benchmarks from our application:
MySQL 5.5 + CentOS 5.2 (XenServer Virtual) = 28 seconds (box is "busy" not buried) MariaDB (5.1) + Windows 2003 (Physical box) = 130 seconds (box is 2% busy) MySQL 5.1 + Windows 2003 (Physical box) = 170 seconds (box is 2% busy) MySQL 5.5 + Windows 2003 (Physical box) = 305 seconds (As high as 600 seconds...) (box is 2% busy)
The only difference between these runs is the removal of skip-locking and the running of mysql_upgrade.exe to update some tables for stored procs on 5.5.
Yes, I know it's a release candidate, I'm feeding that back to MySQL as well.
No slow queries are logged, it doesn't think it's being slow, it just is.
I'm going to start tearing into the queries themselves to see if the INSERT/SELECT plans have gone buggo on 5.5.