As Giuseppe just reminded MySQL 4.0 is reaching its end of life in about 2 weeks from now. When it becomes unsupported by MySQL via normal support agreements together with 3.23 version.
At Percona we do not have such restriction and we will continue to support your environment even if you’re still on MySQL 4 or 3.23 (we indeed do have customers which are still using 3.23 now)
What does it mean for you in practice ? This means we will continue helping you with issues you’re having with MySQL 3.23 or 4.0 and will be happy to backport bug fixes to MySQL 3.23 and 4.0
Supporting MySQL 3.23 and MySQL 4.0 environment is indeed more expensive than current MySQL versions because we can’t relay on Sun/MySQL doing any work with bug fixes plus more work is often needed because these versions have lower transparency than later versions. It also often takes more time to do things because we have to have an extra care to remember all limitations of these versions correctly. For example remember to use set-variable in MySQL 3.23 or remembering all optimizer issues which were fixed more recently.
It costs more to support environments based on 3.23 and 4.0 these days so we would typically recommend to upgrade, however if it is not instantly possible we continue to do support your envinronment. With our simple pricing model of “you pay for consultants true time” we can naturally afford to do it.