Comment by lmm
3 years ago
I don't believe you. Eventual consistency is how the real world works, what possible use case is there where it wouldn't be acceptable? Even if you somehow made the display widget part of the database, you can't make the reader's eyeballs ACID-compliant.
Yeah, I can attest that even banks are really using best effort eventual consistency. However, I think it is very difficult to reason about with systems that try to use eventual consistency as an abstraction. It's a lot easier to think about explicitly when you have one data source/event that propagates outwards through systems with stronger individual guarantees than eventual consistency.
IMO having event streams as first class is the best way to think about things. Then you don't need particularly strong guarantees downstream - think something like Kafka where the only guarantee is that events for the same key will always be processed in order, and it turns out that that's enough to build a system with clear, reliable behaviour that you can reason about quite easily.