Calling it “exactly once” is marketing BS. It’s the same as Oracle claiming for years to support serializable transactions when they didn’t, except that one is technically possible, they just didn’t support it in actuality.
Oracle claiming to support serializable transactions is also false (as you say), but calling it a lie is not the whole story. “ANSI serializable” and actually serializable are not the same thing. Oracle is “ANSI SQL-92 serializable”, as in no named anomalies from the spec. There just happen to be more anomalies like write skew which are not in the spec.
They may never describe Kafka itself without the word "semantics", but here are some other snippets:
- "I know what some of you are thinking. Exactly once delivery is impossible" - "While some have outright said that exactly once delivery is probably impossible!"
They mix their phrasing depending on what they're talking about, and whether they are referring to Kafka directly or indirectly.
They are intentionally using this phrasing to obscure the fact that nothing novel is happening to push sales, and it is absolutely infuriating how well it works.