No, there's no traditional database-level locking here. The Durable Object itself is single-threaded, so you don't have to worry about multiple things trying to change the same data at the same time.

As far as scaling yeah there are still some challenges there. I mentioned in another response there's a limit of 1K RPS, and the single-threadedness could become a bottle-neck. I think there are probably clever workarounds here that we still want to explore, for instance each Durable Object could handle a seperate piece of state and you would effectively have a level of state-based sharding.