KIP-392: preferred-replica hint and local reads

KIP-392: preferred-replica hint and local reads A sequence diagram generated by Archify. Fetch request (includes client.rack=AZ-a) Preferred-replica hint (when available) Match broker.rack and client.rack Re-send fetch request Return data · replication traffic is separate 1. Leader supplies a preferred-replica hint 2. Read locally · fall back to leader if unavailable Consumer · AZ-a · client.rack=AZ-a · Sequence participant Consumer AZ-a · client.rack=AZ-a Leader Broker · AZ-b · Sequence participant Leader Broker AZ-b Follower Broker · AZ-a · Sequence participant Follower Broker AZ-a Legend Data (same AZ) Redirect hint Fetch