Re: Severe performance problem with mysql 5.5.19

[Rick James]

The answer is likely to be in the change notes:
http://dev.mysql.com/doc/relnotes/mysql/5.5/en/
But it will be tedious to read them.
And, read not only the ones up to 5.5.19, but also the ones since then - to see if something was fixed. (Or you could try the latest 5.5.)

Well, the regression could have occurred betwen 5.1.30 and about 5.1.50, at which point 5.5 was RC. (After that point, most fixes to 5.1 were also put into the 5.5 branch.)

If you can isolate a reproducible test case, please post it on
http://bugs.mysql.com