First of all, Thanks for all the input you've given. For me, i will end up using the prefork MPM, and preload most of the modules.

Concerning the memory use of the application, i think Safe::World might help me, i'll look into that.

But for an answer to the question: Can i (force) unload a compiled module from mod-perl, and give back it's memory to the os, the answer would be no i'd guess.

ps.
"You'd end up needing to handle concurrent requests there as well, ..."
Would it not just be an idea to do a request using a unique ticket (id), so all the request are done using some sort of hash? to ensure that the processes could be asynchrone, i'd do a request(uniqueMD5_ID) and expect the result in waitForTheAnswer(uniqueMD5_ID)

Thanks agaim. and have a nice new year all.