Streaming Time and Recovery

Ordering and Multiple Delivery

Distributed messaging can deliver events out of order or deliver the same event more than once.

A consumer can finish its work but fail before acknowledging receipt. The producer may then send the event again because it cannot know whether the first attempt succeeded.

Design the repeated operation so it does not apply the same effect twice. Ordering and deduplication address different problems; one does not automatically provide the other.

Make consumers tolerate the delivery guarantees the platform actually provides. Check ordering where it matters, and prevent a repeated event from applying the same effect twice.