[wuch]

There are perfectly valid reasons to claim that exactly-once delivery is impossible. FLP impossibility result is not one of them. In fact in FLP model solution is trivial, just send the message exactly once and it will be eventually delivered.

* What about network failures? In FLP model network is reliable so there are no network failures.

* What about node failures? In FLP model node failures are permanent, so there is nothing illuminating to say that you cannot deliver message to a node that is permanently offline.

* What if node failures were transient? If network is still reliable and state transitions atomic, then failures are completely unobservable.

* What if state transition are not atomic, and you cannot process message and record that it has been processed in a single step? That would mean that exactly-once delivery is impossible even within a single node, and has nothing to do with distributed nature of computation.

[frankmcsherry]

I'm pretty sure the article claimed no such thing. In fact, the article repeatedly says that it will take no position on whether EO is at all like AB, but that AB is not something you can guarantee (modulo new model assumptions), and probably not something that the Kafka folks should be saying they can do.