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。

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