Comment by TeMPOraL

This. In my testing some years ago, trying to make a basic Roguelike game with the state stored entitely in SQLite, the in-memory db could support reading the visible portion of the map and positions of entities at 60 FPS with time to spare, on a modest machine, and with slight FFI penalty as the code was written in Common Lisp (SBCL). So while you may not want to do this for a first-person shooter, there are many types of games that could in fact live entirely in SQLite, save for some transient visual FX.