kafka 创建 topic

执行 windows 脚本

kafka-topics.bat --create --zookeeper localhost:2181/kafka-zhang --replication-factor 1 --partitions 1 --topic zhang

命令行程序，获取 broker 元数据，计算副本分配方案，然后把 topic 的信息写入 zk

// kafka.zk.AdminZkClient#createTopic
  def createTopic(topic: String,
                  partitions: Int,
                  replicationFactor: Int,
                  topicConfig: Properties = new Properties,
                  rackAwareMode: RackAwareMode = RackAwareMode.Enforced) {
    val brokerMetadatas = getBrokerMetadatas(rackAwareMode)
    val replicaAssignment = AdminUtils.assignReplicasToBrokers(brokerMetadatas, partitions, replicationFactor)
    createOrUpdateTopicPartitionAssignmentPathInZK(topic, replicaAssignment, topicConfig)
  }

KafkaController 监听 zk 节点的变化，并产生 TopicChange 事件 

case object TopicChange extends ControllerEvent {
  override def state: ControllerState = ControllerState.TopicChange

  override def process(): Unit = {
    if (!isActive) return
    val topics = zkClient.getAllTopicsInCluster.toSet
    val newTopics = topics -- controllerContext.allTopics
    val deletedTopics = controllerContext.allTopics -- topics
    controllerContext.allTopics = topics

    registerPartitionModificationsHandlers(newTopics.toSeq)
    val addedPartitionReplicaAssignment = zkClient.getReplicaAssignmentForTopics(newTopics)
    controllerContext.partitionReplicaAssignment = controllerContext.partitionReplicaAssignment.filter(p =>
      !deletedTopics.contains(p._1.topic))
    controllerContext.partitionReplicaAssignment ++= addedPartitionReplicaAssignment
    info(s"New topics: [$newTopics], deleted topics: [$deletedTopics], new partition replica assignment " +
      s"[$addedPartitionReplicaAssignment]")
    if (addedPartitionReplicaAssignment.nonEmpty)
      onNewPartitionCreation(addedPartitionReplicaAssignment.keySet)
  }
}

在 KafkaController.TopicChange#process 中触发 KafkaController#onNewPartitionCreation

// kafka.controller.KafkaController#onNewPartitionCreation  
  private def onNewPartitionCreation(newPartitions: Set[TopicPartition]) {
    info(s"New partition creation callback for ${newPartitions.mkString(",")}")
    partitionStateMachine.handleStateChanges(newPartitions.toSeq, NewPartition)
    replicaStateMachine.handleStateChanges(controllerContext.replicasForPartition(newPartitions).toSeq, NewReplica)
    partitionStateMachine.handleStateChanges(newPartitions.toSeq, OnlinePartition, Option(OfflinePartitionLeaderElectionStrategy))
    replicaStateMachine.handleStateChanges(controllerContext.replicasForPartition(newPartitions).toSeq, OnlineReplica)
  }

partition 状态由 NewPartition 变成 OnlinePartition，会初始化 leader 和 isr 信息，并写入 zk 中，然后发送 LeaderAndIsrRequest 请求通知各 broker。

// kafka.controller.PartitionStateMachine#initializeLeaderAndIsrForPartitions  
  private def initializeLeaderAndIsrForPartitions(partitions: Seq[TopicPartition]): Seq[TopicPartition] = {
    val successfulInitializations = mutable.Buffer.empty[TopicPartition]
    val replicasPerPartition = partitions.map(partition => partition -> controllerContext.partitionReplicaAssignment(partition))
    val liveReplicasPerPartition = replicasPerPartition.map { case (partition, replicas) =>
        val liveReplicasForPartition = replicas.filter(replica => controllerContext.isReplicaOnline(replica, partition))
        partition -> liveReplicasForPartition
    }
    val (partitionsWithoutLiveReplicas, partitionsWithLiveReplicas) = liveReplicasPerPartition.partition { case (_, liveReplicas) => liveReplicas.isEmpty }

    partitionsWithoutLiveReplicas.foreach { case (partition, replicas) =>
      val failMsg = s"Controller $controllerId epoch ${controllerContext.epoch} encountered error during state change of " +
        s"partition $partition from New to Online, assigned replicas are " +
        s"[${replicas.mkString(",")}], live brokers are [${controllerContext.liveBrokerIds}]. No assigned " +
        "replica is alive."
      logFailedStateChange(partition, NewPartition, OnlinePartition, new StateChangeFailedException(failMsg))
    }
    val leaderIsrAndControllerEpochs = partitionsWithLiveReplicas.map { case (partition, liveReplicas) =>
      val leaderAndIsr = LeaderAndIsr(liveReplicas.head, liveReplicas.toList)
      val leaderIsrAndControllerEpoch = LeaderIsrAndControllerEpoch(leaderAndIsr, controllerContext.epoch)
      partition -> leaderIsrAndControllerEpoch
    }.toMap
    val createResponses = try {
      zkClient.createTopicPartitionStatesRaw(leaderIsrAndControllerEpochs)
    } catch {
      case e: Exception =>
        partitionsWithLiveReplicas.foreach { case (partition,_) => logFailedStateChange(partition, partitionState(partition), NewPartition, e) }
        Seq.empty
    }
    createResponses.foreach { createResponse =>
      val code = createResponse.resultCode
      val partition = createResponse.ctx.get.asInstanceOf[TopicPartition]
      val leaderIsrAndControllerEpoch = leaderIsrAndControllerEpochs(partition)
      if (code == Code.OK) {
        controllerContext.partitionLeadershipInfo.put(partition, leaderIsrAndControllerEpoch)
        controllerBrokerRequestBatch.addLeaderAndIsrRequestForBrokers(leaderIsrAndControllerEpoch.leaderAndIsr.isr,
          partition, leaderIsrAndControllerEpoch, controllerContext.partitionReplicaAssignment(partition), isNew = true)
        successfulInitializations += partition
      } else {
        logFailedStateChange(partition, NewPartition, OnlinePartition, code)
      }
    }
    successfulInitializations
  }  

最后把 replica 状态由 NewReplica 变成 OnlineReplica，至此，topic 创建完成。