Let's say I make a client-server application. A simple game for example. Where each client polls the server every half a minute. How many clients is it possible to have before it overlaods a wamp server? Basically how robust is Apache for this kind of stuff? Getting a request, aggregating data from mysql server, and then returning the data in an xml format. What solution should I use for my case? Thank you in advance.
That depends a lot on your hardware and also configuration. In my general experience:
However, instead of polling, you may want to consider a different game architecture. Maybe you want to have the data pushed to the clients instead. That can help with reducing load.
I would say that if you build the game you are building, you may have not chosen the right architecture.