Spark一级资源调度Shedule机制及SpreadOut模式源码深入剖析

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Spark商业环境实战-Spark一级资源调度Shedule机制及SpreadOut模式源码深入剖析
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1 Shedule 在哪里？干什么？

Shedule()发生在Master中，那么Master都负责什么呢？可以看到只要发生以下任何事件，就会重新执行Shedule()

RegisterWorker
RegisterApplication
ExecutorStateChanged
RequestSubmitDriver
completeRecovery
relaunchDriver
removeApplication
handleRequestExecutors
handleKillExecutors
removeDriver

因此，可以看出所谓的一级资源调度，在Local-cluster部署模式和Standalone部署模式中，其实就是基于Master实现的资源调度，更确切的说是对Driver的资源调度和对Application(参数指定数量的Executor)的资源调度。

2 Master的天子王权（除Yarn资源和K8s容器编排）

Master是Local-cluster部署模式和Standalone部署模式中，最为核心的管理组件。Master将直接决定整个集群的可用性，容错性，可用性。可谓位于整个Spark集群中最重要，最核心的位置。职责如下：

Worker的管理
Application的管理
Driver的管理
统一管理和分配集群中的资源（如内存和cpu）
接收各个Worker的注册，状态更新，心跳
Driver和Application的注册

3 Driver 的前世今生？是什么？如何纳管？

Driver的诞生来源于Master接收到RequestSubmitDriver请求，那么RequestSubmitDriver来源于何处，这又要从SparkSubmit类说起，先上代码段，看看STANDALONE_CLUSTER_SUBMIT_CLASS，就从这里开始：

    private[deploy] val YARN_CLUSTER_SUBMIT_CLASS = "org.apache.spark.deploy.yarn.YarnClusterApplication"   private[deploy] val REST_CLUSTER_SUBMIT_CLASS = classOf[RestSubmissionClientApp].getName()private[deploy] val STANDALONE_CLUSTER_SUBMIT_CLASS = classOf[ClientApp].getName()private[deploy] val KUBERNETES_CLUSTER_SUBMIT_CLASS ="org.apache.spark.deploy.k8s.submit.KubernetesClientApplication"
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这里开始封装Spark-submit提交的各个参数，同时在StandAlone模式下，我们开始关注ClientEndpoint它是一个终端.

  // In standalone cluster mode, use the REST client to submit the application (Spark 1.3+).// All Spark parameters are expected to be passed to the client through system properties.if (args.isStandaloneCluster) {if (args.useRest) {childMainClass = REST_CLUSTER_SUBMIT_CLASSchildArgs += (args.primaryResource, args.mainClass)} else {// In legacy standalone cluster mode, use Client as a wrapper around the user classchildMainClass = STANDALONE_CLUSTER_SUBMIT_CLASS   <= 神来之笔ClientAppif (args.supervise) { childArgs += "--supervise" }Option(args.driverMemory).foreach { m => childArgs += ("--memory", m) }Option(args.driverCores).foreach { c => childArgs += ("--cores", c) }childArgs += "launch"childArgs += (args.master, args.primaryResource, args.mainClass)}if (args.childArgs != null) {childArgs ++= args.childArgs}}
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ClientApp （ClientEndpoint）开始向Master异步发送RequestSubmitDriver请求，也就是说：一次Spark-Submit提交，就会发送一次RequestSubmitDriver请求，进而生成一个资源申请的Driver。

 val driverDescription = new DriverDescription(driverArgs.jarUrl,driverArgs.memory,driverArgs.cores,driverArgs.supervise,command)asyncSendToMasterAndForwardReply[SubmitDriverResponse](RequestSubmitDriver(driverDescription))
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Master接收到提交的资源申请，开始向自己的成员变量drivers中放入一个Driver，也即每一次任务提交的的资源申请驱动。

   case RequestSubmitDriver(description) =>if (state != RecoveryState.ALIVE) {val msg = s"${Utils.BACKUP_STANDALONE_MASTER_PREFIX}: $state. " +"Can only accept driver submissions in ALIVE state."context.reply(SubmitDriverResponse(self, false, None, msg))} else {logInfo("Driver submitted " + description.command.mainClass)val driver = createDriver(description)persistenceEngine.addDriver(driver)waitingDrivers += driverdrivers.add(driver)schedule()// TODO: It might be good to instead have the submission client poll the master to determine//       the current status of the driver. For now it's simply "fire and forget".context.reply(SubmitDriverResponse(self, true, Some(driver.id),s"Driver successfully submitted as ${driver.id}"))}
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封装资源申请实体DriverInfo

private def createDriver(desc: DriverDescription): DriverInfo = {val now = System.currentTimeMillis()val date = new Date(now)new DriverInfo(now, newDriverId(date), desc, date)
}
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总结：Master的receiveAndReply方法接收ClientEndpoint发送的消息RequestSubmitDriver，将收到的Driver注册到waitingDrivers。基于此，才会有后面的基于Driver的一级资源调度。

  RequestSubmitDriver详情请参考这篇博客，比我的更详细。https://blog.csdn.net/u011564172/article/details/68496848
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4 Application 的前世今生？和Driver渊源？如何纳管？

差一点就疯了，Application和Driver完全不是一个概念。Driver的诞生发生在Spark-submit阶段。而Application的诞生发生在DAG调度阶段，也即SparkContext实例化阶段。拼了非讲清不可。

Master 最终会根据Application的资源申请，把appDesc放入apps队列中，并对Application进行资源调度。

  val appDesc = ApplicationDescription(sc.appName, maxCores, sc.executorMemory, command,webUrl, sc.eventLogDir, sc.eventLogCodec, coresPerExecutor, initialExecutorLimit)SparkContext：SparkContext -> StandaloneSchedulerBackend -> StandaloneAppClient.start() -> registerWithMaster -> masterRef.send(RegisterApplication(appDescription, self)) -> Master:-> apps += app ->shedule()[Driver启动后，调用startExecutorsOnWorkers()->allocateWorkerResourceToExecutors]
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Master端点registerApplication

private def registerApplication(app: ApplicationInfo): Unit = { val appAddress = app.driver.address if (addressToApp.contains(appAddress)) { logInfo("Attempted to re-register application at same address: " + appAddress) return }
```
  applicationMetricsSystem.registerSource(app.appSource)apps += appidToApp(app.id) = appendpointToApp(app.driver) = appaddressToApp(appAddress) = appwaitingApps += app
}
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```

5 Master的职责再讲

首先集群启动之后，Worker会向Master注册，同时携带身份标识和资源情况（如ID,host，port,cpu核数，内存大小），那么这些资源交由Master纳管后，Master会按照一定的资源调度策略分配给Driver和Application。
Master给Driver分配完资源后，将会向Worker发送启动Driver命令，Worker接收到命令后，开始启动Driver。
Master给Application分配完资源后，将向Worker发送启动Executor命令，Worker接收到命令后，开始启动Executor。

6 Shedule()神秘面纱

6.1 Shedule 核心思想

打乱洗牌存活的Worker,在Worker资源满足的情况下，启动Executor。
神来之笔（Driver资源调度）==> launchDriver(worker, driver)

神来之笔（Executor调度）==> startExecutorsOnWorkers()

    * Schedule the currently available resources among waiting apps. This method will be called* every time a new app joins or resource availability changes.private def schedule(): Unit = {if (state != RecoveryState.ALIVE) {return}// Drivers take strict precedence over executorsval shuffledAliveWorkers = Random.shuffle(workers.toSeq.filter(_.state == WorkerState.ALIVE))val numWorkersAlive = shuffledAliveWorkers.sizevar curPos = 0for (driver <- waitingDrivers.toList) { // iterate over a copy of waitingDrivers// We assign workers to each waiting driver in a round-robin fashion. For each driver, we// start from the last worker that was assigned a driver, and continue onwards until we have// explored all alive workers.var launched = falsevar numWorkersVisited = 0while (numWorkersVisited < numWorkersAlive && !launched) {val worker = shuffledAliveWorkers(curPos)numWorkersVisited += 1if (worker.memoryFree >= driver.desc.mem && worker.coresFree >= driver.desc.cores) {launchDriver(worker, driver)      <= 神来之笔（Driver资源调度）waitingDrivers -= driverlaunched = true}curPos = (curPos + 1) % numWorkersAlive}}startExecutorsOnWorkers()               <= 神来之笔（Executor调度）}
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6.2 launchDriver 挖一挖

发送到Worker开始启动driver

private def launchDriver(worker: WorkerInfo, driver: DriverInfo) {logInfo("Launching driver " + driver.id + " on worker " + worker.id)worker.addDriver(driver)driver.worker = Some(worker)worker.endpoint.send(LaunchDriver(driver.id, driver.desc))driver.state = DriverState.RUNNING
}
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Worker端的回馈

   case LaunchDriver(driverId, driverDesc) =>logInfo(s"Asked to launch driver $driverId")val driver = new DriverRunner(conf,driverId,workDir,sparkHome,driverDesc.copy(command = Worker.maybeUpdateSSLSettings(driverDesc.command, conf)),self,workerUri,securityMgr)drivers(driverId) = driverdriver.start()coresUsed += driverDesc.coresmemoryUsed += driverDesc.mem
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6.3 startExecutorsOnWorkers 钻一钻

coresPerExecutor：参数设置的每一个Executor所使用的内核数，默认为1。
app.desc.memoryPerExecutorMB ：参数设置的ExecutorMemory。
scheduleExecutorsOnWorkers ：返回各个Worker上分配的内核数

allocateWorkerResourceToExecutors：

  private def startExecutorsOnWorkers(): Unit = {// Right now this is a very simple FIFO scheduler. We keep trying to fit in the first app// in the queue, then the second app, etc.for (app <- waitingApps) {val coresPerExecutor = app.desc.coresPerExecutor.getOrElse(1) <= 神来之笔（Worker资源情况判断）// If the cores left is less than the coresPerExecutor,the cores left will not be allocatedif (app.coresLeft >= coresPerExecutor) {// Filter out workers that don't have enough resources to launch an executorval usableWorkers = workers.toArray.filter(_.state == WorkerState.ALIVE).filter(worker => worker.memoryFree >= app.desc.memoryPerExecutorMB &&worker.coresFree >= coresPerExecutor).sortBy(_.coresFree).reverse                 <= 神来之笔（Worker资源情况判断）val assignedCores = scheduleExecutorsOnWorkers(app, usableWorkers, spreadOutApps) <= 神来之笔// Now that we've decided how many cores to allocate on each worker, let's allocate themfor (pos <- 0 until usableWorkers.length if assignedCores(pos) > 0) {allocateWorkerResourceToExecutors(app, assignedCores(pos), app.desc.coresPerExecutor, usableWorkers(pos)) <= 神来之笔}}}}
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6.3 scheduleExecutorsOnWorkers 较较真

   * Schedule executors to be launched on the workers.* Returns an array containing number of cores assigned to each worker.** There are two modes of launching executors. The first attempts to spread out an application's* executors on as many workers as possible, while the second does the opposite (i.e. launch them* on as few workers as possible). The former is usually better for data locality purposes and is* the default.** The number of cores assigned to each executor is configurable. When this is explicitly set,* multiple executors from the same application may be launched on the same worker if the worker* has enough cores and memory. Otherwise, each executor grabs all the cores available on the* worker by default, in which case only one executor per application may be launched on each* worker during one single schedule iteration.* Note that when `spark.executor.cores` is not set, we may still launch multiple executors from* the same application on the same worker. Consider appA and appB both have one executor running* on worker1, and appA.coresLeft > 0, then appB is finished and release all its cores on worker1,* thus for the next schedule iteration, appA launches a new executor that grabs all the free* cores on worker1, therefore we get multiple executors from appA running on worker1.** It is important to allocate coresPerExecutor on each worker at a time (instead of 1 core* at a time). Consider the following example: cluster has 4 workers with 16 cores each.* User requests 3 executors (spark.cores.max = 48, spark.executor.cores = 16). If 1 core is* allocated at a time, 12 cores from each worker would be assigned to each executor.* Since 12 < 16, no executors would launch [SPARK-8881].
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spreadOutApps 决定了Executor的分配是集中的，还是按照顺序分散的。
oneExecutorPerWorker ：如果没有指定coresPerExecutor，那么就说明每一个Worker上只有一个Executor，否则就是多个
assignedCores(pos)是返回的数组，其中freeWorkers就是索引0,1,2。对应的可分配的Cores就会是指定Worker上能够分配的。

allocateWorkerResourceToExecutors:就是根据打散后的Worker索引，进行Executor的启动，玄机在于每一个Worker是否需要启动多个Executor

  private def scheduleExecutorsOnWorkers(app: ApplicationInfo,usableWorkers: Array[WorkerInfo],spreadOutApps: Boolean): Array[Int] = {val coresPerExecutor = app.desc.coresPerExecutorval minCoresPerExecutor = coresPerExecutor.getOrElse(1)val oneExecutorPerWorker = coresPerExecutor.isEmptyval memoryPerExecutor = app.desc.memoryPerExecutorMBval numUsable = usableWorkers.lengthval assignedCores = new Array[Int](numUsable) // Number of cores to give to each workerval assignedExecutors = new Array[Int](numUsable) // Number of new executors on each workervar coresToAssign = math.min(app.coresLeft, usableWorkers.map(_.coresFree).sum)/** Return whether the specified worker can launch an executor for this app. */def canLaunchExecutor(pos: Int): Boolean = {val keepScheduling = coresToAssign >= minCoresPerExecutorval enoughCores = usableWorkers(pos).coresFree - assignedCores(pos) >= minCoresPerExecutor// If we allow multiple executors per worker, then we can always launch new executors.// Otherwise, if there is already an executor on this worker, just give it more cores.val launchingNewExecutor = !oneExecutorPerWorker || assignedExecutors(pos) == 0if (launchingNewExecutor) {val assignedMemory = assignedExecutors(pos) * memoryPerExecutorval enoughMemory = usableWorkers(pos).memoryFree - assignedMemory >= memoryPerExecutorval underLimit = assignedExecutors.sum + app.executors.size < app.executorLimitkeepScheduling && enoughCores && enoughMemory && underLimit} else {// We're adding cores to an existing executor, so no need// to check memory and executor limitskeepScheduling && enoughCores}}// Keep launching executors until no more workers can accommodate any// more executors, or if we have reached this application's limitsvar freeWorkers = (0 until numUsable).filter(canLaunchExecutor)while (freeWorkers.nonEmpty) {freeWorkers.foreach { pos =>var keepScheduling = truewhile (keepScheduling && canLaunchExecutor(pos)) {coresToAssign -= minCoresPerExecutorassignedCores(pos) += minCoresPerExecutor// If we are launching one executor per worker, then every iteration assigns 1 core// to the executor. Otherwise, every iteration assigns cores to a new executor.if (oneExecutorPerWorker) {assignedExecutors(pos) = 1} else {assignedExecutors(pos) += 1}// Spreading out an application means spreading out its executors across as// many workers as possible. If we are not spreading out, then we should keep// scheduling executors on this worker until we use all of its resources.// Otherwise, just move on to the next worker.if (spreadOutApps) {keepScheduling = false}}}freeWorkers = freeWorkers.filter(canLaunchExecutor)}assignedCores}
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6.3 allocateWorkerResourceToExecutors 探究竟

通知Worker根据Application的要求，也即根据应用提交时的要求，开始启动Executor。

  private def allocateWorkerResourceToExecutors(app: ApplicationInfo,assignedCores: Int,coresPerExecutor: Option[Int],worker: WorkerInfo): Unit = {// If the number of cores per executor is specified, we divide the cores assigned// to this worker evenly among the executors with no remainder.// Otherwise, we launch a single executor that grabs all the assignedCores on this worker.val numExecutors = coresPerExecutor.map { assignedCores / _ }.getOrElse(1)val coresToAssign = coresPerExecutor.getOrElse(assignedCores)for (i <- 1 to numExecutors) {val exec = app.addExecutor(worker, coresToAssign)launchExecutor(worker, exec)app.state = ApplicationState.RUNNING}
}
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Master 终端发送 LaunchExecutor

  private def launchExecutor(worker: WorkerInfo, exec: ExecutorDesc): Unit = {logInfo("Launching executor " + exec.fullId + " on worker " + worker.id)worker.addExecutor(exec)worker.endpoint.send(LaunchExecutor(masterUrl,exec.application.id, exec.id, exec.application.desc, exec.cores, exec.memory))exec.application.driver.send(ExecutorAdded(exec.id, worker.id, worker.hostPort, exec.cores, exec.memory))}
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7 总结

至此，一级资源调度Shedule机制剖析完毕，真的是剖析的体无完肤啊。贴一张图，该休息了。因为已经0:18了。

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