That's true, but using Apache::compat is somewhat slow because of the extra work it does to emulate mod_perl 1 functions. It's meant as a temporary stopgap to port old code to mp 2.

UPDATE: I asked for opinions about this on the mod_perl list, and the answer I got was that Apache::compat is problematic because it makes some code written to the actual mod_perl 2 API not work. Also, it uses a bit more memory than Registry because it loads a whole bunch of optional modules. Actual performance comparisons are hard to draw though, since it depends on which functions you use. Some functions simulated in Apache::compat are going to be significantly slower than they were in mod_perl 1, but not all of them.

The full response is here.