Kafka源码系列教程之删除topic

前言

Apache Kafka发源于LinkedIn，于2011年成为Apache的孵化项目，随后于2012年成为Apache的主要项目之一。Kafka使用Scala和Java进行编写。Apache Kafka是一个快速、可扩展的、高吞吐、可容错的分布式发布订阅消息系统。Kafka具有高吞吐量、内置分区、支持数据副本和容错的特性，适合在大规模消息处理场景中使用。

本文依然是以kafka0.8.2.2为例讲解

一，如何删除一个topic

删除一个topic有两个关键点：

1，配置删除参数

delete.topic.enable这个Broker参数配置为True。

2，执行

bin/kafka-topics.sh --zookeeper zk_host:port/chroot --delete --topic my_topic_name

假如不配置删除参数为true的话，topic其实并没有被清除，只是被标记为删除。此时，估计一般人的做法是删除topic在Zookeeper的信息和日志，其实这个操作并不会清除kafkaBroker内存的topic数据。所以，此时最佳的策略是配置删除参数为true然后，重启kafka。

二，重要的类介绍

1，PartitionStateMachine

该类代表分区的状态机。决定者分区的当前状态，和状态转移。四种状态

• NonExistentPartition
• NewPartition
• OnlinePartition
• OfflinePartition

2，ReplicaManager

负责管理当前机器的所有副本，处理读写、删除等具体动作。

读写：写获取partition对象，再获取Replica对象，再获取Log对象，采用其管理的Segment对象将数据写入、读出。

3，ReplicaStateMachine

副本的状态机。决定者副本的当前状态和状态之间的转移。一个副本总共可以处于一下几种状态的一种
NewReplica：Crontroller在分区重分配的时候可以创建一个新的副本。只能接受变为follower的请求。前状态可以是NonExistentReplica

OnlineReplica：新启动的分区，能接受变为leader或者follower请求。前状态可以是NewReplica, OnlineReplica or OfflineReplica

OfflineReplica：死亡的副本处于这种状态。前状态可以是NewReplica, OnlineReplica

ReplicaDeletionStarted：分本删除开始的时候处于这种状态，前状态是OfflineReplica

ReplicaDeletionSuccessful：副本删除成功。前状态是ReplicaDeletionStarted

ReplicaDeletionIneligible：删除失败的时候处于这种状态。前状态是ReplicaDeletionStarted

NonExistentReplica：副本成功删除之后处于这种状态，前状态是ReplicaDeletionSuccessful

4，TopicDeletionManager

该类管理着topic删除的状态机

1)，TopicCommand通过创建/admin/delete_topics/<topic>，来发布topic删除命令。

2)，Controller监听/admin/delete_topic子节点变动，开始分别删除topic

3)，Controller有个后台线程负责删除Topic

三，源码彻底解析topic的删除过程

此处会分四个部分：

A),客户端执行删除命令作用

B),不配置delete.topic.enable整个流水的源码

C),配置了delete.topic.enable整个流水的源码

D),手动删除zk上topic信息和磁盘数据

1，客户端执行删除命令

bin/kafka-topics.sh --zookeeper zk_host:port/chroot --delete --topic my_topic_name

进入kafka-topics.sh我们会看到

exec $(dirname $0)/kafka-run-class.sh kafka.admin.TopicCommand $@

进入TopicCommand里面，main方法里面

else if(opts.options.has(opts.deleteOpt))
 deleteTopic(zkClient, opts)

实际内容是

val topics = getTopics(zkClient, opts)
if (topics.length == 0) {
 println("Topic %s does not exist".format(opts.options.valueOf(opts.topicOpt)))
}
topics.foreach { topic =>
 try {
 ZkUtils.createPersistentPath(zkClient, ZkUtils.getDeleteTopicPath(topic))

在"/admin/delete_topics"目录下创建了一个topicName的节点。

2，假如不配置delete.topic.enable整个流水是

总共有两处listener会响应：

A),TopicChangeListener

B),DeleteTopicsListener

使用topic的删除命令删除一个topic的话，指挥触发DeleteTopicListener。

var topicsToBeDeleted = {
 import JavaConversions._
 (children: Buffer[String]).toSet
}
val nonExistentTopics = topicsToBeDeleted.filter(t => !controllerContext.allTopics.contains(t))
topicsToBeDeleted --= nonExistentTopics
if(topicsToBeDeleted.size > 0) {
 info("Starting topic deletion for topics " + topicsToBeDeleted.mkString(","))
 // mark topic ineligible for deletion if other state changes are in progress
 topicsToBeDeleted.foreach { topic =>
 val preferredReplicaElectionInProgress =
  controllerContext.partitionsUndergoingPreferredReplicaElection.map(_.topic).contains(topic)
 val partitionReassignmentInProgress =
  controllerContext.partitionsBeingReassigned.keySet.map(_.topic).contains(topic)
 if(preferredReplicaElectionInProgress || partitionReassignmentInProgress)
  controller.deleteTopicManager.markTopicIneligibleForDeletion(Set(topic))
 }
 // add topic to deletion list
 controller.deleteTopicManager.enqueueTopicsForDeletion(topicsToBeDeleted)
}

由于都会判断delete.topic.enable是否为true，假如不为true就不会执行，为true就进入执行

controller.deleteTopicManager.markTopicIneligibleForDeletion(Set(topic))
controller.deleteTopicManager.enqueueTopicsForDeletion(topicsToBeDeleted)

3，delete.topic.enable配置为true

此处与步骤2的区别，就是那两个处理函数。

controller.deleteTopicManager.markTopicIneligibleForDeletion(Set(topic))
controller.deleteTopicManager.enqueueTopicsForDeletion(topicsToBeDeleted)

markTopicIneligibleForDeletion函数的处理为

if(isDeleteTopicEnabled) {
 val newTopicsToHaltDeletion = topicsToBeDeleted & topics
 topicsIneligibleForDeletion ++= newTopicsToHaltDeletion
 if(newTopicsToHaltDeletion.size > 0)
 info("Halted deletion of topics %s".format(newTopicsToHaltDeletion.mkString(",")))
}

主要是停止删除topic，假如存储以下三种情况

* Halt delete topic if -
* 1. replicas being down
* 2. partition reassignment in progress for some partitions of the topic
* 3. preferred replica election in progress for some partitions of the topic

enqueueTopicsForDeletion主要作用是更新删除topic的集合，并激活TopicDeleteThread

def enqueueTopicsForDeletion(topics: Set[String]) {
 if(isDeleteTopicEnabled) {
 topicsToBeDeleted ++= topics
 partitionsToBeDeleted ++= topics.flatMap(controllerContext.partitionsForTopic)
 resumeTopicDeletionThread()
 }
}

在删除线程DeleteTopicsThread的doWork方法中

topicsQueuedForDeletion.foreach { topic =>
// if all replicas are marked as deleted successfully, then topic deletion is done
 if(controller.replicaStateMachine.areAllReplicasForTopicDeleted(topic)) {
 // clear up all state for this topic from controller cache and zookeeper
 completeDeleteTopic(topic)
 info("Deletion of topic %s successfully completed".format(topic))
 }

进入completeDeleteTopic方法中

// deregister partition change listener on the deleted topic. This is to prevent the partition change listener
// firing before the new topic listener when a deleted topic gets auto created
partitionStateMachine.deregisterPartitionChangeListener(topic)
val replicasForDeletedTopic = controller.replicaStateMachine.replicasInState(topic, ReplicaDeletionSuccessful)
// controller will remove this replica from the state machine as well as its partition assignment cache
replicaStateMachine.handleStateChanges(replicasForDeletedTopic, NonExistentReplica)
val partitionsForDeletedTopic = controllerContext.partitionsForTopic(topic)
// move respective partition to OfflinePartition and NonExistentPartition state
partitionStateMachine.handleStateChanges(partitionsForDeletedTopic, OfflinePartition)
partitionStateMachine.handleStateChanges(partitionsForDeletedTopic, NonExistentPartition)
topicsToBeDeleted -= topic
partitionsToBeDeleted.retain(_.topic != topic)
controllerContext.zkClient.deleteRecursive(ZkUtils.getTopicPath(topic))
controllerContext.zkClient.deleteRecursive(ZkUtils.getTopicConfigPath(topic))
controllerContext.zkClient.delete(ZkUtils.getDeleteTopicPath(topic))
controllerContext.removeTopic(topic)

主要作用是解除掉监控分区变动的listener，删除Zookeeper具体节点信息，删除磁盘数据，更新内存数据结构，比如从副本状态机里面移除分区的具体信息。

其实，最终要的是我们的副本磁盘数据是如何删除的。我们重点介绍这个部分。

首次清除的话，在删除线程DeleteTopicsThread的doWork方法中

{
 // if you come here, then no replica is in TopicDeletionStarted and all replicas are not in
 // TopicDeletionSuccessful. That means, that either given topic haven't initiated deletion
 // or there is at least one failed replica (which means topic deletion should be retried).
 if(controller.replicaStateMachine.isAnyReplicaInState(topic, ReplicaDeletionIneligible)) {
 // mark topic for deletion retry
 markTopicForDeletionRetry(topic)
 }

进入markTopicForDeletionRetry

val failedReplicas = controller.replicaStateMachine.replicasInState(topic, ReplicaDeletionIneligible)
info("Retrying delete topic for topic %s since replicas %s were not successfully deleted"
 .format(topic, failedReplicas.mkString(",")))
controller.replicaStateMachine.handleStateChanges(failedReplicas, OfflineReplica)

在ReplicaStateMachine的handleStateChanges方法中，调用了handleStateChange，处理OfflineReplica

// send stop replica command to the replica so that it stops fetching from the leader
brokerRequestBatch.addStopReplicaRequestForBrokers(List(replicaId), topic, partition, deletePartition = false)

接着在handleStateChanges中

brokerRequestBatch.sendRequestsToBrokers(controller.epoch, controllerContext.correlationId.getAndIncrement)

给副本数据存储节点发送StopReplicaKey副本指令，并开始删除数据

stopReplicaRequestMap foreach { case(broker, replicaInfoList) =>
 val stopReplicaWithDelete = replicaInfoList.filter(p => p.deletePartition == true).map(i => i.replica).toSet
 val stopReplicaWithoutDelete = replicaInfoList.filter(p => p.deletePartition == false).map(i => i.replica).toSet
 debug("The stop replica request (delete = true) sent to broker %d is %s"
 .format(broker, stopReplicaWithDelete.mkString(",")))
 debug("The stop replica request (delete = false) sent to broker %d is %s"
 .format(broker, stopReplicaWithoutDelete.mkString(",")))
 replicaInfoList.foreach { r =>
 val stopReplicaRequest = new StopReplicaRequest(r.deletePartition,
  Set(TopicAndPartition(r.replica.topic, r.replica.partition)), controllerId, controllerEpoch, correlationId)
 controller.sendRequest(broker, stopReplicaRequest, r.callback)
 }
}
stopReplicaRequestMap.clear()

Broker的KafkaApis的Handle方法在接受到指令后

case RequestKeys.StopReplicaKey => handleStopReplicaRequest(request)

val (response, error) = replicaManager.stopReplicas(stopReplicaRequest)

接着是在stopReplicas方法中

{
 controllerEpoch = stopReplicaRequest.controllerEpoch
 // First stop fetchers for all partitions, then stop the corresponding replicas
 replicaFetcherManager.removeFetcherForPartitions(stopReplicaRequest.partitions.map(r => TopicAndPartition(r.topic, r.partition)))
 for(topicAndPartition <- stopReplicaRequest.partitions){
 val errorCode = stopReplica(topicAndPartition.topic, topicAndPartition.partition, stopReplicaRequest.deletePartitions)
 responseMap.put(topicAndPartition, errorCode)
 }
 (responseMap, ErrorMapping.NoError)
}

进一步进入stopReplica方法，正式进入日志删除

getPartition(topic, partitionId) match {
 case Some(partition) =>
 if(deletePartition) {
  val removedPartition = allPartitions.remove((topic, partitionId))
  if (removedPartition != null)
  removedPartition.delete() // this will delete the local log
 }

以上就是kafka的整个日志删除流水。

4，手动删除zk上topic信息和磁盘数据

TopicChangeListener会监听处理，但是处理很简单，只是更新了

val deletedTopics = controllerContext.allTopics -- currentChildren
controllerContext.allTopics = currentChildren

val addedPartitionReplicaAssignment = ZkUtils.getReplicaAssignmentForTopics(zkClient, newTopics.toSeq)
controllerContext.partitionReplicaAssignment = controllerContext.partitionReplicaAssignment.filter(p =>

四，总结

Kafka的topic的删除过程，实际上就是基于Zookeeper做了一个订阅发布系统。Zookeeper的客户端创建一个节点/admin/delete_topics/<topic>，由kafka Controller监听到事件之后正式触发topic的删除：解除Partition变更监听的listener，清除内存数据结构，删除副本数据，删除topic的相关Zookeeper节点。

delete.topic.enable配置该参数为false的情况下执行了topic的删除命令，实际上未做任何动作。我们此时要彻底删除topic建议修改该参数为true，重启kafka，这样topic信息会被彻底删除，已经测试。

一般流行的做法是手动删除Zookeeper的topic相关信息及磁盘数据但是这样的话会造成部分内存数据未清除。至于是否会有隐患，未测试。

好了，以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对我们的支持。