3 ms·

You should let the Apache Flink team know, they mention exactly-once processing on their home page (under "correctness guarantees") and in their list of feature

• sethammons 2y ago
  A common mistake: Exactly once delivery is not the same as exactly once processing. Exactly once delivery is an impossibility; see the two generals problem. Exactly once processing is usually at-least-once delivery coupled with deduplication or an otherwise idempotent action
• Fire-Dragon-DoL 2y ago
  They are not the first or the last. You CAN have "at most once" processing, since there is always the option of processing zero messages due to systems being down, but it's a joint effort, nobody is able to offer it "for free" (as in, no effort to implement it)