What server architecture is appropriate for a multiplayer online game?

Solution 1:

Best known example is EVE Online, which uses Stackless Python. They have written they own server.

Their architecture described:

• http://highscalability.com/eve-online-architecture
• http://www.massively.com/2008/09/28/eve-evolved-eve-onlines-server-model/
• http://www.slideshare.net/Arbow/stackless-python-in-eve

Generally I recommend reading highscalability.com, specially the real world examples.

Solution 2:

Since you're already doing Java, you might want to take a look at Sun's DarkStar project:

I don't know any commercial games using it (I believe it's still in development).