You don’t even need to involve deletes; if all of these happen “simultaneously”:
- client A appends “a” to list L
- client B appends “b” to list L
- client C appends “c” to list L
the server will arbitrarily apply the appends in some order, and then send the result back to the clients. But, each of the clients has applied its append locally and is showing those results until it gets different information from the server, so the next time step might be
- client A thinks L is [“a”]
- client B thinks L is [“b”]
- client C thinks L is [“c”]
- server sends state event to clients saying that L is [“c”,”b”,”a”]
Then when the clients receive the state from the server, I guess they all discard their pending mutations and use the state from the server as their state of the world. But what if each of the three appends results in that client winning the game if their mutation gets applied first? Do all the clients display “you win” for 300ms while waiting for the server’s update?
We have the "game-winning" scenario on the reflect.net homepage right now: https://reflect.net/. It's a puzzle and when the last piece is placed, it shows a celebration and the puzzle resets moments later. But we only want that logic to run once. We can't do this client-side because there are many people and we'd end up having to choose a leader or something. This is the same exact situation as wanting to show in the UI who won (who placed the last piece) and only wanting to do that once.
Reflect has first-class support for this kind of situation by allowing mutators to run special code server-side. I talk about this a bit here:
You modified the operations, I specifically chose a scenario where User C (in my example) introduces an undecidable situation. Appends are trivial to solve.
>If your answer is like "we just send them the whole array again", this breaks the transactional model (x2).
True. I was thinking of a simpler criticism that, if it held, would also make Reflect less useful. aboodman replied in the sibling that (of course) they thought of that, so my criticism doesn't apply.
