Leadership transfer (graceful step down)

Leadership transfer, also referred to as graceful leader step down, is a concept from the Raft dissertation (Section 3.10: Leadership transfer extension) where a leader can select a replica to "take over" as leader, and gracefully transfer leadership to that node by engineering an election in which that node is highly likely to win. This minimizes the period in a leadership change during which there is no recognized leader, and therefore minimizes latency spikes during a leader change.

This feature can be useful when the leader replica should be removed from the tablet configuration. This can happen when the tablet server running the leader replica is being decommissioned, or in the case of tablet replica rebalancing where the tablet server hosting the leader replica can be considered overloaded.