I am talking about only one (an ideal of course) connection to the database.
If you mean one persistent connection per user (per instance of the application), then I see where you are going, but one single connection to the database full stop seems like a waste of the ability of the DB to handle multiple connections (as yuo may have multiple users).
I still don't see how this is going to be much benifit: you still have to associate a request with a user, which is more of a bother than whether the PHP files are loaded from memory or from files - hell, why not just use the Zend Encoder and have the encoded files stored in memory? Seems much easier to do with the benifit that it will speed up any PHP application. Infact, I can hardly see why the servlet hosting code overhead is going to make anything faster than this anyway!