I wrote an application in PHP using the Symfony Framework. Now that the traffic to my site is growing, I really need to recompile it with HipHop PHP.
Is it possible to do it? After recompiling it, do I need to use fastcgi module to run it?
I don't wish to sound pretentious but are you really going to have a site the size of facebook? Majority of large websites don't use HipHop. They just use efficient caching (Varnish for example), good database optimisation(indexes in the right places etc.), and code accelerators(such as APC) I don't think you will really notice much of a difference if you did decide to use HipHop. Bare in mind that a lot of PHP functions don't work in HipHop also.
If you're using Symfony2, have you looked into ESI (Edge Side Includes)?
Just my thoughts, but really I don't think it'll be worth the headache to use HipHop.