You are looking for a fairly simple game, multiplayer and using a database

I'd like to be able to experiment with a game for which code is available for free, where I can build and run the game and, of course, also deploy the database needed to support the game's network aspect.

Thus, a multiplayer game based on the trick could apply here (vs. an FPS). Any type of database-dependent game for appropriate multiplayer aspects, such as player data, session data, and so on. It can even be a relatively static game content.

I want to experiment with caches to see if I can modify the game to use a cache instead of hitting the database, to see the differences in performance and experience.

My question is, which game or games would be appropriate for this bill?