That's a lot of ads for the book, but inbetween the author describes event sourcing. There is still state, but with event sourcing it does not need to be persis

That's a lot of ads for the book, but inbetween the author describes event sourcing. There is still state, but with event sourcing it does not need to be persisted, and so it can live entirely in process' memory - thus no database is needed.