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I agree. I wish more messaging platforms would recognize this and stop trying to paper-over the failure mode (Kafka just came out with "Exactly Once," which I think is a variant of the 2-Phase-Commit protocol, which still does not solve the problem).

My go-to for explaining to people is the Two Generals Problem https://en.wikipedia.org/wiki/Two_Generals%27_Problem




After watching the video from the Kafka Summit talk https://www.confluent.io/kafka-summit-nyc17/introducing-exac...

it's an essentially-useless guarantee for any sort of Kafka consumer that interacts with an external system.

Exactly-Once is not something that can be provided-for or delegated-to an arbitrary, non-integrated system. For an "integrated" system, it requires idempotent behavior, in which case it's really At-Least-Once, so...




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