KIP-1166 — Improve high-watermark replication

Accepted Kafka 4.1 Broker

Propagates the follower's current high-watermark (HWM) in the KRaft Fetch request so the leader can immediately complete parked Fetch requests when only the HWM has advanced (without new records). KRaft could not distinguish whether a follower was behind on records versus behind on HWM, so it unconditionally parked Fetch requests for up to 500ms even when only the HWM needed propagation, causing admin operation metadata updates to appear delayed by up to 500ms.

Protocol Impact

Fetch v18

Details