kafka 各模块启动全流程 KafkaServer
【代码入口】
kafka 新增了 raft 协议之后将 BrokerServer、ControlServer 使用了单独的文件来启动最终调用网络层和请求处理层，如果还是使用 zk 的方式启动则是 KafkaServer 启动网络层和请求处理层。
主要区别：
private def buildServer(props: Properties): Server = {
val config = KafkaConfig.fromProps(props, false)
// 直接启动定时任务、网络层、请求处理层
if (config.requiresZookeeper) {
new KafkaServer(
config,
Time.SYSTEM,
threadNamePrefix = None,
enableForwarding = false
)
}
// 调用 BrokerServer 等来启动网络层和请求处理层
else {
new KafkaRaftServer(
config,
Time.SYSTEM,
threadNamePrefix = None
)
}
}虽然中间过程不一样，但是最终还是调用的相同的请求处理器来进行处理。
【启动流程】
下面是使用 zk 的启动流程：
系统启动入口：
Kafka.getPropsFromArgs() 读取启动参数 (kafka.Kafka$)
Kafka.buildServer() 服务端实例启动 (kafka.Kafka$)
KafkaServer.startup() 服务端启动 (kafka.server.KafkaServer)
创建一些定时任务，KafkaScheduler.schedule() 中传入一个函数周期执行，大致分类：
KafkaScheduler.schedule() 执行定时任务 name=transactionalId-expiration (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=isr-expiration (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=__consumer_offsets-3 (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=delete-expired-group-metadata (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=highwatermark-checkpoint (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=PeriodicProducerExpirationCheck (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=kafka-log-start-offset-checkpoint (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=kafka-log-retention (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=auto-leader-rebalance-task (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=kafka-delete-logs (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=shutdown-idle-replica-alter-log-dirs-thread (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=kafka-log-flusher (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=kafka-recovery-point-checkpoint (kafka.utils.KafkaScheduler)
KafkaScheduler.schedule() 执行定时任务 name=transaction-abort (kafka.utils.KafkaScheduler)初始化并启动网络模块，根据图解可以看到默认每个端点会创建一个 Acceptor、三个 Processor、RequestChannel 。其中 Acceptor 负责处理链接请求、Processor 负责处理业务请求、RequestChannel 缓存两个队列保存请求和响应：
RequestChannel.new() 初始化请求通道 (kafka.network.RequestChannel)
SockerServer.startup() 网络启动 (kafka.network.SocketServer)
SocketServer.createDataPlaneAcceptorsAndProcessors() 创建 Acceptor/Processor (kafka.network.SocketServer)
SocketServer.createAcceptor() 为每个EndPoint创建客户端连接处理器Acceptor,endPoint=EndPoint(null,9092,ListenerName(PLAINTEXT),PLAINTEXT) (kafka.network.SocketServer)
SocketServer.openServerSocket() (kafka.network.Acceptor)
SocketServer.addDataPlaneProcessors() newProcessorsPerListener=3 (kafka.network.SocketServer)
SocketServer.newProcessor() id=0,requestChannel=kafka.network.RequestChannel@4d0402b (kafka.network.SocketServer)
RequestChannel.addProcessor() 缓存当前 processor (kafka.network.RequestChannel)
SocketServer.newProcessor() id=1,requestChannel=kafka.network.RequestChannel@4d0402b (kafka.network.SocketServer)
RequestChannel.addProcessor() 缓存当前 processor (kafka.network.RequestChannel)
SocketServer.newProcessor() id=2,requestChannel=kafka.network.RequestChannel@4d0402b (kafka.network.SocketServer)
RequestChannel.addProcessor() 缓存当前 processor (kafka.network.RequestChannel)同时创建 KafkaRequestHandler 请求业务处理器（8个），创建业务处理线程池 KafkaRequestHandlerPool（8个线程），这个对象从前面的请求队列中取出后交给 Api 对象处理。
KafkaRequestHandlerPool.new() 创建请求处理池 brokerId=1,numThreads=8 (kafka.server.KafkaRequestHandlerPool)
KafkaRequestHandler.createHandler() id=0 (kafka.server.KafkaRequestHandlerPool)
KafkaRequestHandler.createHandler() id=1 (kafka.server.KafkaRequestHandlerPool)
KafkaRequestHandler.createHandler() id=2 (kafka.server.KafkaRequestHandlerPool)
KafkaRequestHandler.createHandler() id=3 (kafka.server.KafkaRequestHandlerPool)
KafkaRequestHandler.createHandler() id=4 (kafka.server.KafkaRequestHandlerPool)
KafkaRequestHandler.createHandler() id=5 (kafka.server.KafkaRequestHandlerPool)
KafkaRequestHandler.createHandler() id=6 (kafka.server.KafkaRequestHandlerPool)
KafkaRequestHandler.createHandler() id=7 (kafka.server.KafkaRequestHandlerPool)这八个业务线程处理器各自调用 run() 从请求响应 RequestChannel 队列中进行轮训，将轮训到的请求交给 KafkaApis 进行处理：
KafkaRequestHandler.run() 调用[requestChannel]从[requestQueue]中轮询客户端请求 (kafka.server.KafkaRequestHandler)
最终处理请求的对象是 KafkaApis.handle()：
KafkaApis.handle() 处理客户端请求 (kafka.server.KafkaApis)
前面业务请求处理器已经开始运行并不断从队列缓存中轮训请求了，就等客户端链接并发送请求了。所以下一步是一个 Acceptor、三个 Processor的启动。
其中 Acceptor 是 whille 轮训监听 OP_ACCEPT 事件，新建立的链接加入 newConnections 缓存中，Processor 是遍历这些链接并为每个链接轮训可读事件。
SocketServer.startDataPlaneProcessorsAndAcceptors() (kafka.network.SocketServer)
SocketServer.startAcceptorAndProcessors() (kafka.network.SocketServer)
SocketServer.run() 开始运行Server主任务 (kafka.network.Processor)
SocketServer.run() 开始运行Server主任务 (kafka.network.Processor)
SocketServer.run() 开始运行Server主任务 (kafka.network.Processor)
SocketServer.run() (kafka.network.Acceptor)
SocketServer.acceptNewConnections() 死while循环监听客户端链接,注册 SelectionKey.OP_ACCEPT 事件 (kafka.network.Acceptor)接下来是等待客户端链接，轮训请求并加入缓存队列，等待上面的 KafkaRequestHandler 和 KafkaApis 进行处理：
SocketServer.configureNewConnections() 从newConnections队列中获取到新的连接 (kafka.network.Processor)
Selector.register() 绑定SocketChannel,id=127.0.0.1:9092-127.0.0.1:40264-0 (org.apache.kafka.common.network.Selector)
SocketServer.processCompletedReceives() 调用selector轮询到的客户端请求 (kafka.network.Processor)
RequestChannel.Request() 将请求添加到requestQueue队列,等待KafkaApis (kafka.network.RequestChannel)【数据请求和控制请求区别】
在启动启动过程中会启动两个 Plane，分别是 DataPlane、ControlPlane。作用不同，网络模块启动入口
SocketServer.startup() => 启动网络模块
SocketServer.createControlPlaneAcceptorAndProcessor() => 启动控制类请求处理器模块
SocketServer.startControlPlaneProcessorAndAcceptor() => 启动 Acceptor、Processor
SocketServer.createDataPlaneAcceptorsAndProcessors() => 启动数据请求类处理器模块
SocketServer.startDataPlaneProcessorsAndAcceptors() => 启动 Acceptor、Processor两个都一样，创建 Acceptor、Processor 并启动。
【一些关键步骤】
1. Acceptor、Processor 的启动入口，以及客户端链接、请求、响应处理的入口。
SocketServer.startAcceptorAndProcessors() 会遍历每个 Processor，分别各自执行 KafkaServer.run()：
override def run(): Unit = {
startupComplete()
try {
while (isRunning) {
try {
// 轮训新链接,保存到 newConnections 中并将新连接列表中的连接注册到 Selector 上
configureNewConnections()
// 将响应列表中的响应存入连接缓存，注册监听可写事件SelectionKey.OP_WRITE
processNewResponses()
// 便利 newConnections每个链接,并轮训每个连接上的可读事件，将网络数据暂存到接收缓冲区
poll()
// 将上一步接收缓冲区的网络数据解析为 Kafka 请求，并将其扔进请求队列，等待请求处理器轮询处理
processCompletedReceives()
// 处理响应
processCompletedSends()
processDisconnected()
closeExcessConnections()
} catch {
case e: Throwable => processException("Processor got uncaught exception.", e)
}
}
} finally {
debug(s"Closing selector - processor $id")
CoreUtils.swallow(closeAll(), this, Level.ERROR)
shutdownComplete()
}
}2.请求的分发流程。其中请求处理的基类是 ApiRequestHandler，两个子类分别是 KafkaApis、ControllerApis。分别处理消息请求、元数据请求。
KafkaApis.handler() 会根据不同的请求进行消息路由处理：
override def handle(request: RequestChannel.Request): Unit = {
try {
if (!apiVersionManager.isApiEnabled(request.header.apiKey)) {
throw new IllegalStateException(s"API ${request.header.apiKey} is not enabled")
}
request.header.apiKey match {
case ApiKeys.PRODUCE => handleProduceRequest(request)
case ApiKeys.FETCH => handleFetchRequest(request)
case ApiKeys.LIST_OFFSETS => handleListOffsetRequest(request)
case ApiKeys.METADATA => handleTopicMetadataRequest(request)
case ApiKeys.LEADER_AND_ISR => handleLeaderAndIsrRequest(request)
case ApiKeys.STOP_REPLICA => handleStopReplicaRequest(request)
case ApiKeys.UPDATE_METADATA => handleUpdateMetadataRequest(request)
case ApiKeys.CONTROLLED_SHUTDOWN => handleControlledShutdownRequest(request)
case ApiKeys.OFFSET_COMMIT => handleOffsetCommitRequest(request)
case ApiKeys.OFFSET_FETCH => handleOffsetFetchRequest(request)
case ApiKeys.FIND_COORDINATOR => handleFindCoordinatorRequest(request)
case ApiKeys.JOIN_GROUP => handleJoinGroupRequest(request)
case ApiKeys.HEARTBEAT => handleHeartbeatRequest(request)
case ApiKeys.LEAVE_GROUP => handleLeaveGroupRequest(request)
case ApiKeys.SYNC_GROUP => handleSyncGroupRequest(request)
case ApiKeys.DESCRIBE_GROUPS => handleDescribeGroupRequest(request)
case ApiKeys.LIST_GROUPS => handleListGroupsRequest(request)
case ApiKeys.SASL_HANDSHAKE => handleSaslHandshakeRequest(request)
case ApiKeys.API_VERSIONS => handleApiVersionsRequest(request)
case ApiKeys.CREATE_TOPICS => maybeForwardToController(request, handleCreateTopicsRequest)
case ApiKeys.DELETE_TOPICS => maybeForwardToController(request, handleDeleteTopicsRequest)
case ApiKeys.DELETE_RECORDS => handleDeleteRecordsRequest(request)
case ApiKeys.INIT_PRODUCER_ID => handleInitProducerIdRequest(request)
case ApiKeys.OFFSET_FOR_LEADER_EPOCH => handleOffsetForLeaderEpochRequest(request)
case ApiKeys.ADD_PARTITIONS_TO_TXN => handleAddPartitionToTxnRequest(request)
case ApiKeys.ADD_OFFSETS_TO_TXN => handleAddOffsetsToTxnRequest(request)
case ApiKeys.END_TXN => handleEndTxnRequest(request)
case ApiKeys.WRITE_TXN_MARKERS => handleWriteTxnMarkersRequest(request)
case ApiKeys.TXN_OFFSET_COMMIT => handleTxnOffsetCommitRequest(request)
case ApiKeys.DESCRIBE_ACLS => handleDescribeAcls(request)
case ApiKeys.CREATE_ACLS => maybeForwardToController(request, handleCreateAcls)
case ApiKeys.DELETE_ACLS => maybeForwardToController(request, handleDeleteAcls)
case ApiKeys.ALTER_CONFIGS => maybeForwardToController(request, handleAlterConfigsRequest)
case ApiKeys.DESCRIBE_CONFIGS => handleDescribeConfigsRequest(request)
case ApiKeys.ALTER_REPLICA_LOG_DIRS => handleAlterReplicaLogDirsRequest(request)
case ApiKeys.DESCRIBE_LOG_DIRS => handleDescribeLogDirsRequest(request)
case ApiKeys.SASL_AUTHENTICATE => handleSaslAuthenticateRequest(request)
case ApiKeys.CREATE_PARTITIONS => maybeForwardToController(request, handleCreatePartitionsRequest)
case ApiKeys.CREATE_DELEGATION_TOKEN => maybeForwardToController(request, handleCreateTokenRequest)
case ApiKeys.RENEW_DELEGATION_TOKEN => maybeForwardToController(request, handleRenewTokenRequest)
case ApiKeys.EXPIRE_DELEGATION_TOKEN => maybeForwardToController(request, handleExpireTokenRequest)
case ApiKeys.DESCRIBE_DELEGATION_TOKEN => handleDescribeTokensRequest(request)
case ApiKeys.DELETE_GROUPS => handleDeleteGroupsRequest(request)
case ApiKeys.ELECT_LEADERS => handleElectReplicaLeader(request)
case ApiKeys.INCREMENTAL_ALTER_CONFIGS => maybeForwardToController(request, handleIncrementalAlterConfigsRequest)
case ApiKeys.ALTER_PARTITION_REASSIGNMENTS => maybeForwardToController(request, handleAlterPartitionReassignmentsRequest)
case ApiKeys.LIST_PARTITION_REASSIGNMENTS => handleListPartitionReassignmentsRequest(request)
case ApiKeys.OFFSET_DELETE => handleOffsetDeleteRequest(request)
case ApiKeys.DESCRIBE_CLIENT_QUOTAS => handleDescribeClientQuotasRequest(request)
case ApiKeys.ALTER_CLIENT_QUOTAS => maybeForwardToController(request, handleAlterClientQuotasRequest)
case ApiKeys.DESCRIBE_USER_SCRAM_CREDENTIALS => handleDescribeUserScramCredentialsRequest(request)
case ApiKeys.ALTER_USER_SCRAM_CREDENTIALS => maybeForwardToController(request, handleAlterUserScramCredentialsRequest)
case ApiKeys.ALTER_ISR => handleAlterIsrRequest(request)
case ApiKeys.UPDATE_FEATURES => maybeForwardToController(request, handleUpdateFeatures)
case ApiKeys.ENVELOPE => handleEnvelope(request)
case ApiKeys.DESCRIBE_CLUSTER => handleDescribeCluster(request)
case ApiKeys.DESCRIBE_PRODUCERS => handleDescribeProducersRequest(request)
case ApiKeys.UNREGISTER_BROKER => maybeForwardToController(request, handleUnregisterBrokerRequest)
case _ => throw new IllegalStateException(s"No handler for request api key ${request.header.apiKey}")
}
} catch {
case e: FatalExitError => throw e
case e: Throwable => requestHelper.handleError(request, e)
} finally {
// try to complete delayed action. In order to avoid conflicting locking, the actions to complete delayed requests
// are kept in a queue. We add the logic to check the ReplicaManager queue at the end of KafkaApis.handle() and the
// expiration thread for certain delayed operations (e.g. DelayedJoin)
replicaManager.tryCompleteActions()
// The local completion time may be set while processing the request. Only record it if it's unset.
if (request.apiLocalCompleteTimeNanos < 0)
request.apiLocalCompleteTimeNanos = time.nanoseconds
}
}3.请求响应处理流程。首先是将响应进行返回，然后缓存 response 对象在响应返回之后执行 onComplete() 一些回调逻辑。
首先看 SocketServer.processNewResponses() 循环从响应队列中 poll 看是否有需要响应的 Response 对象。代码如下：
private def processNewResponses(): Unit = {
var currentResponse: RequestChannel.Response = null
// responseQueue.poll() 循环调用从响应队列中获取需要处理的 Response 对象
while ({currentResponse = dequeueResponse(); currentResponse != null}) {
val channelId = currentResponse.request.context.connectionId
try {
currentResponse match {
case response: NoOpResponse =>
updateRequestMetrics(response)
handleChannelMuteEvent(channelId, ChannelMuteEvent.RESPONSE_SENT)
tryUnmuteChannel(channelId)
// 如果需要返回给客户端,则调用 sendResponse() 进行响应
case response: SendResponse =>
sendResponse(response, response.responseSend)
case response: CloseConnectionResponse =>
updateRequestMetrics(response)
trace("Closing socket connection actively according to the response code.")
close(channelId)
case _: StartThrottlingResponse =>
handleChannelMuteEvent(channelId, ChannelMuteEvent.THROTTLE_STARTED)
case _: EndThrottlingResponse =>
handleChannelMuteEvent(channelId, ChannelMuteEvent.THROTTLE_ENDED)
tryUnmuteChannel(channelId)
case _ =>
throw new IllegalArgumentException(s"Unknown response type: ${currentResponse.getClass}")
}
} catch {
case e: Throwable =>
processChannelException(channelId, s"Exception while processing response for $channelId", e)
}
}
}接着调用 sendResponse() 进行响应，同时将已经 send 的 Response 对象缓存到 inflightResponses，后面会轮询这个 map 取出响应处理一些回调操作。
SocketServer.sendResponse() 代码如下：
protected[network] def sendResponse(response: RequestChannel.Response, responseSend: Send): Unit = {
val connectionId = response.request.context.connectionId if (channel(connectionId).isEmpty) {
response.request.updateRequestMetrics(0L, response)
}
if (openOrClosingChannel(connectionId).isDefined) {
// 先将响应发送给客户端
selector.send(new NetworkSend(connectionId, responseSend))
// 再将响应缓存到 inflightResponses 中,后续执行一些回调操作
inflightResponses += (connectionId -> response)
}
}同时 Process 进程也就是 KafkaServer.run() 会处理这些响应的回调逻辑，调用的是 SocketServer.processCompletedSends() 。
SocketServer.processCompletedSends() 代码如下：
private def processCompletedSends(): Unit = {
// 遍历所有的 List<NetworkSend> 这个用于处理客户端响应之后的回调逻辑
selector.completedSends.forEach { send =>
try {
// 从缓存中取出 Response 对象,通过 destinationId 进行查找
val response = inflightResponses.remove(send.destinationId).getOrElse {
throw new IllegalStateException(s"Send for ${send.destinationId} completed, but not in `inflightResponses`")
}
updateRequestMetrics(response)
// 然后调用 Response.onComplete() 执行响应之后的回调逻辑
response.onComplete.foreach(onComplete => onComplete(send))
handleChannelMuteEvent(send.destinationId, ChannelMuteEvent.RESPONSE_SENT)
tryUnmuteChannel(send.destinationId)
} catch {
case e: Throwable => processChannelException(send.destinationId,
s"Exception while processing completed send to ${send.destinationId}", e)
}
}
selector.clearCompletedSends()
}4.定时任务的作用，根据 KafkaScheduler 定时任务大致分类如下：
执行定时任务 name=transaction-abort (kafka.utils.KafkaScheduler) 定期放弃超时了（默认1min）的事务。
执行定时任务 name=transactionalId-expiration (kafka.utils.KafkaScheduler) 定期放弃超时了的事务（默认1min），移除事务id。
执行定时任务 name=isr-expiration (kafka.utils.KafkaScheduler) 用于将超过 replicaLagTimeMaxMs 的同步时间的 replica 从 ISR 中移除。
执行定时任务 name=__consumer_offsets-3 (kafka.utils.KafkaScheduler)
执行定时任务 name=delete-expired-group-metadata (kafka.utils.KafkaScheduler) 用于默认 60s 一次 清除 group 的 offsets。
执行定时任务 name=highwatermark-checkpoint (kafka.utils.KafkaScheduler) 定期持久化 partition 的Hight Watermark值。
执行定时任务 name=PeriodicProducerExpirationCheck (kafka.utils.KafkaScheduler)
执行定时任务 name=kafka-log-start-offset-checkpoint (kafka.utils.KafkaScheduler) 将所有日志的当前日志开始偏移量写到日志目录中的文本文件中，以避免暴露已被 DeleteRecordsRequest 删除的数据。
执行定时任务 name=kafka-log-retention (kafka.utils.KafkaScheduler) 周期性检测不符合保留条件的 log。
执行定时任务 name=kafka-delete-logs (kafka.utils.KafkaScheduler) 周期性将上面检测后标记为删除的log进行删除。
执行定时任务 name=auto-leader-rebalance-task (kafka.utils.KafkaScheduler) 负责维护分区的优先副本的均衡。
执行定时任务 name=shutdown-idle-replica-alter-log-dirs-thread (kafka.utils.KafkaScheduler)
执行定时任务 name=kafka-log-flusher (kafka.utils.KafkaScheduler) 定期flush日志，也就是异步刷盘。
执行定时任务 name=kafka-recovery-point-checkpoint (kafka.utils.KafkaScheduler) 用于定期更新每个 log 目录名下的 recovery-point-offset-checkpoint 文件，记录了最后一次检查点，之前的日志都已经落盘。
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