[jira] [Created] (KAFKA-10197) Elect preferred leader when completing a partition reassignment

["Bob Barrett (Jira)" <ji...@apache.org>]

Bob Barrett created KAFKA-10197:
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             Summary: Elect preferred leader when completing a partition reassignment
                 Key: KAFKA-10197
                 URL: https://issues.apache.org/jira/browse/KAFKA-10197
             Project: Kafka
          Issue Type: Improvement
            Reporter: Bob Barrett


Currently, when completing a partition reassignment, we elect a leader from the new replica assignment without requiring that the leader be the new preferred leader. Instead, we just choose any in-sync replica:
{code:java}
private def leaderForReassign(partition: TopicPartition,
                              leaderAndIsr: LeaderAndIsr,
                              controllerContext: ControllerContext): ElectionResult = { 
  val targetReplicas = controllerContext.partitionFullReplicaAssignment(partition).targetReplicaAssignment.replicas
  val liveReplicas = targetReplicas.filter(replica => controllerContext.isReplicaOnline(replica, partition))
  val isr = leaderAndIsr.isr
  val leaderOpt = PartitionLeaderElectionAlgorithms.reassignPartitionLeaderElection(targetReplicas, isr, liveReplicas.toSet)
  val newLeaderAndIsrOpt = leaderOpt.map(leader => leaderAndIsr.newLeader(leader, isUnclean = false))
  ElectionResult(partition, newLeaderAndIsrOpt, targetReplicas)
}
{code}
If auto preferred leader election is enabled, the preferred leader will eventually be elected. However, it would make sense to choose the preferred leader after the reassignment without waiting for the automatic trigger.

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