This is pretty cool stuff. I have been working with Apache Flink where the computational model is exactly once (which is still hugely useful) but it still comes

This is pretty cool stuff. I have been working with Apache Flink where the computational model is exactly once (which is still hugely useful) but it still comes with caveats about duplicate messages downstream, which makes writing to downstream db or having multiple flink processes tricky. Often times this is done by windowing data and producing complete snapshots of that window (i.e. you need to keep all the state for a given window) such that the message downstream is idempotent and then aggregating windows together (which can be non trivial for certain aggregations). Once flink (and other systems) support this, I think it will really be a game changer. It will allow for doing things like sending an increment downstream rather than needing to keep all that state. Instead of mostly seeing stream processing as a thing we do for analytic use cases, it can really become the backbone for streaming applications. Event Sourcing/CQRS has been an idea for a while, but in practice, is difficult to do because to the inherent difficulty in dealing with message semantics and consistency (see https://data-artisans.com/blog/drivetribe-cqrs-apache-flink https://data-artisans.com/blog/drivetribe-cqrs-apache-flink for a good write up about such an app). The ability to independently optimize for both reads and writes while also not having to make all messages be idempotent, in my mind, will make this feasible for a broad range of teams and won't require a huge amount of work in thinking up clever message formats or working through as many failure scenarios. That being said, I fully expect this to bite hard when the caveats aren't understood (such as when interacting with external databases) and there are still other hard problems. Like creating a consistent down stream view of an app in terms of business events rather than hooking into a database transaction log. Still though, I think these are the sort of solutions needed to make distributed systems easier, even though there are lots of caveats :)