You can just pick a database you like to work with and OpenFire will put it's data inside it. Chose the wrong database for your project? Switching databases is no problem! Just want to play? OpenFire runs without a database by default!
OpenFire holds some very clever algorithms under it's belt, and stores objects in highly optimized fragments. Combined with realtime, serial data transfer, reading as well as writing objects wil be incredibly fast.
OpenFire supports full-blown realtime data pushes that is significantly faster than communicating trough HTTP. User have a older browser like IE7 or some crappy browser like that? Fine, then we use long-polling!