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  1. Kafka
  2. KAFKA-5480

Partition Leader may not be elected although there is one live replica in ISR

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    Details

    • Type: Bug
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: 0.9.0.1, 0.10.2.0
    • Fix Version/s: None
    • Component/s: replication
    • Labels:

      Description

      Currently we found a consumer blocking in the poll because of the coordinator of this consumer group is not available.
      Digging in the log, we found some of the __consumer_offsets' partitions' leader are -1, so the coordinator not available is
      because of leader is not available, the scene is as follow:
      There are 3 brokers in the cluster, and the network of the cluster is not stable. At the beginning, the partition [__consumer_offsets,3]
      Leader is 3, ISR is [3, 1, 2]
      1. Broker 1 become the controller:
      [2017-06-10 15:48:30,006] INFO [Controller 1]: Broker 1 starting become controller state transition (kafka.controller.KafkaController)
      [2017-06-10 15:48:30,085] INFO [Controller 1]: Initialized controller epoch to 8 and zk version 7 (kafka.controller.KafkaController)
      [2017-06-10 15:48:30,088] INFO [Controller 1]: Controller 1 incremented epoch to 9 (kafka.controller.KafkaController)

      2. Broker 2 soon becomes the controller, it is aware of all the brokers:
      [2017-06-10 15:48:30,936] INFO [Controller 2]: Broker 2 starting become controller state transition (kafka.controller.KafkaController)
      [2017-06-10 15:48:30,936] INFO [Controller 2]: Initialized controller epoch to 9 and zk version 8 (kafka.controller.KafkaController)
      [2017-06-10 15:48:30,943] INFO [Controller 2]: Controller 2 incremented epoch to 10 (kafka.controller.KafkaController)

      [2017-06-10 15:48:31,574] INFO [Controller 2]: Currently active brokers in the cluster: Set(1, 2, 3) (kafka.controller.KafkaController)
      [2017-06-10 15:48:31,574] INFO [Controller 2]: Currently shutting brokers in the cluster: Set() (kafka.controller.KafkaController)
      So broker 2 think Leader 3 is alive, does not need to elect leader.

      3. Broker 1 is not resign until 15:48:32, but it is not aware of the broker 3:
      [2017-06-10 15:48:31,470] INFO [Controller 1]: List of partitions to be deleted: Map() (kafka.controller.KafkaController)
      [2017-06-10 15:48:31,470] INFO [Controller 1]: Currently active brokers in the cluster: Set(1, 2) (kafka.controller.KafkaController)
      [2017-06-10 15:48:31,470] INFO [Controller 1]: Currently shutting brokers in the cluster: Set() (kafka.controller.KafkaController)

      and change the Leader to broker 1:
      [2017-06-10 15:48:31,847] DEBUG [OfflinePartitionLeaderSelector]: Some broker in ISR is alive for [__consumer_offsets,3]. Select 1 from ISR 1,2 to be the leader. (kafka.controller.OfflinePartitionLeaderSelector)

      broker 1 resign until 15:48:32 when the zk client is aware of the broker 2 has change the controller's data:
      kafka.common.ControllerMovedException: Broker 1 received update metadata request with correlation id 4 from an old controller 1 with epoch 9. Latest known controller epoch is 10
      at kafka.server.ReplicaManager.maybeUpdateMetadataCache(ReplicaManager.scala:621)
      at kafka.server.KafkaApis.handleUpdateMetadataRequest(KafkaApis.scala:163)
      at kafka.server.KafkaApis.handle(KafkaApis.scala:76)
      at kafka.server.KafkaRequestHandler.run(KafkaRequestHandler.scala:60)
      at java.lang.Thread.run(Thread.java:748)
      [2017-06-10 15:48:32,307] INFO New leader is 2 (kafka.server.ZookeeperLeaderElector$LeaderChangeListener)

      4. Then broker 2's controllerContext.partitionLeadershipInfo cached the Leader is 3 ISR is [3,1,2], but in zk
      Leader is 1 ISR is [1, 2]. It will keep this a long time until another zk event happen.

      5. After 1 day, broker 2 received the broker 1's broker change event:
      [2017-06-12 21:43:18,287] INFO [BrokerChangeListener on Controller 2]: Broker change listener fired for path /brokers/ids with children 2,3 (kafka.controller.ReplicaStateMachine$BrokerChangeListener)
      [2017-06-12 21:43:18,293] INFO [BrokerChangeListener on Controller 2]: Newly added brokers: , deleted brokers: 1, all live brokers: 2,3 (kafka.controller.ReplicaStateMachine$BrokerChangeListener)

      then broker 2 will invoke onBrokerFailure for the deleted broker 1, but because Leader is 3, it will not change the partition to OfflinePartition and will not change the leader in partitionStateMachine.triggerOnlinePartitionStateChange().
      But in the replicaStateMachine.handleStateChanges(activeReplicasOnDeadBrokers, OfflineReplica), it will remove the replica 1 in ISR.
      In the removeReplicaFromIsr, controller will read the ISR from zk again, will find Leader change to 1, then it will change
      the partition's leader to -1 and ISR [2]:

      [2017-06-12 21:43:19,158] DEBUG [Controller 2]: Removing replica 1 from ISR 1,3,2 for partition [__consumer_offsets,3]. (kafka.controller.KafkaController)
      [2017-06-12 21:43:19,160] INFO [Controller 2]: New leader and ISR for partition [__consumer_offsets,3] is

      {"leader":-1,"leader_epoch":15,"isr":[2]}

      (kafka.controller.KafkaController)

      So the [__consumer_offsets,3] partition's leader is -1, although replica 2 is alive and in ISR, it will keep this a long time until another relative zk event happen, for example, reboot one of the broker who have the replicas.

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            • Assignee:
              Unassigned
              Reporter:
              pengwei Pengwei
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              • Created:
                Updated: