小记--------spark资源调度机制源码分析-----Schedule

Posted 2020-11-26 yzqyxq

Master类位置所在：spark-core_2.11-2.1.0.jar的org.apache.spark.deploy.master下的Master类

/**
* driver调度机制原理代码分析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 = {
 
  //首先判断，master撞他提不是ALIVE的话， 就直接返回
  //也就是说 standby master是不会进行application等资源的调度的
  if (state != RecoveryState.ALIVE) {
    return
  }
 
  // Rondom.shuffle的原理，就是对传入的集合的元素进行随机的打乱
  // 取出了workers中的所有值钱注册上来的worker，进行过滤， 必须死活状态为ALIVE的worker
  // 对状态为ALIVE的worker， 调用Random的shuffle方法进行随机的打乱
  val shuffledAliveWorkers = Random.shuffle(workers.toSeq.filter(_.state == WorkerState.ALIVE))
 
  // 获取到当前可用worker的个数
  val numWorkersAlive = shuffledAliveWorkers.size
  var curPos = 0
 
  // 只有用yarn-cluster模式提交的时候，才会注册driver，因为standalone和yarn-client模式，都会在本地直接启动driver，而不会来注册driver，更不会让master调度driver了
   
    // 首先会遍历waitingDrivers 这个ArrayBuffer 
  for (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 = false
    var numWorkersVisited = 0
       
     // while的条件，numWorkersVisited小于numWorkersAlive，就是说只要还有活着的worker没有被遍历到，那么就继续遍历。而且，当前这个driver还没有被启动，也就是launched为false
     while (numWorkersVisited < numWorkersAlive && !launched) {
      val worker = shuffledAliveWorkers(curPos)
      numWorkersVisited += 1
 
      // 如果当前这个worker的空闲内存量大于等于driver需要的内存
      // 并且worker的空闲CPU数量大于等于driver需要的CPU数量
      if (worker.memoryFree >= driver.desc.mem && worker.coresFree >= driver.desc.cores) {
 
        //那么启动driver
        launchDriver(worker, driver)//详细代码见代码1
 
        // 并且将driver从waitingDrivers队列中移除
        waitingDrivers -= driver
        launched = true
      }
    
      //然后将指针指向下一个worker
      curPos = (curPos + 1) % numWorkersAlive
    }
  }
  startExecutorsOnWorkers()
}
 
 
代码1
/**
 *在某一个worker上启动driver
 */
private def launchDriver(worker: WorkerInfo, driver: DriverInfo) {
  logInfo("Launching driver " + driver.id + " on worker " + worker.id)
 
  // 将driver加入worker内存的缓存结构中
  // 将worker内使用的内存和CPU数量，都加上driver需要的内存和CPU数量
  worker.addDriver(driver)
 
  // 同时把worker也加入到driver内部的缓存结构中  进行一个互相引用，互相能找到对方
  driver.worker = Some(worker)
 
  // 然后调用worker的线程，给它发送LaunchDriver消息，让worker来启动driver
  worker.endpoint.send(LaunchDriver(driver.id, driver.desc))
 
  // 然后将driver的状态设置为RUNNING
  driver.state = DriverState.RUNNING
}
 
 
 
//executor调度原理及源码分析
/**
* Schedule and launch executors on workers
*/
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.
  // 首先遍历出waitingApps中的ApplicationInfo，并且过滤出还有需要调用的core的Application
  for (app <- waitingApps if app.coresLeft > 0) {
    val coresPerExecutor: Option[Int] = app.desc.coresPerExecutor
   
     // Filter out workers that don‘t have enough resources to launch an executor
     // 从workers中，过滤出状态为ALIVE的，再次过滤可以被Application使用的worker，然后按照剩余CPU数量倒序排序
    val usableWorkers = workers.toArray.filter(_.state == WorkerState.ALIVE)
      .filter(worker => worker.memoryFree >= app.desc.memoryPerExecutorMB &&
        worker.coresFree >= coresPerExecutor.getOrElse(1))
      .sortBy(_.coresFree).reverse
    val assignedCores = scheduleExecutorsOnWorkers(app, usableWorkers, spreadOutApps)//详细代码见：代码2
 
 
    // Now that we‘ve decided how many cores to allocate on each worker, let‘s allocate them
    // 给每个worker分配完Application要求的CPU core之后 ， 遍历每个worker
    // 并且判断之前给这个worker分配到了CPU core
    for (pos <- 0 until usableWorkers.length if assignedCores(pos) > 0) {
 
      //在Application内部缓存中添加executor
      allocateWorkerResourceToExecutors(
        app, assignedCores(pos), coresPerExecutor, usableWorkers(pos))//详细代码见：代码3
    }
  }
}
 
代码2
private def scheduleExecutorsOnWorkers(
    app: ApplicationInfo,
    usableWorkers: Array[WorkerInfo],
    spreadOutApps: Boolean): Array[Int] = {
  val coresPerExecutor = app.desc.coresPerExecutor
 
  // 每个executor上最小的cores数量，默认为1
  val minCoresPerExecutor = coresPerExecutor.getOrElse(1)
  val oneExecutorPerWorker = coresPerExecutor.isEmpty
  val memoryPerExecutor = app.desc.memoryPerExecutorMB
 
// 可用的worker数量
  val numUsable = usableWorkers.length
  val assignedCores = new Array[Int](numUsable) // Number of cores to give to each worker
  val assignedExecutors = new Array[Int](numUsable) // Number of new executors on each worker
 
// 取Application需要的core是和集群workers的空闲cores和的最小值
  var coresToAssign = math.min(app.coresLeft, usableWorkers.map(_.coresFree).sum)
 
 
  /** Return whether the specified worker can launch an executor for this app. */
// 是否可以在一个worker上分配Executor
  def canLaunchExecutor(pos: Int): Boolean = {
    val keepScheduling = coresToAssign >= minCoresPerExecutor
    val 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) == 0
 
// 检查worker的空闲core和内存是否够用
    if (launchingNewExecutor) {
      val assignedMemory = assignedExecutors(pos) * memoryPerExecutor
      val enoughMemory = usableWorkers(pos).memoryFree - assignedMemory >= memoryPerExecutor
      val underLimit = assignedExecutors.sum + app.executors.size < app.executorLimit
      keepScheduling && enoughCores && enoughMemory && underLimit
    } else {
      // We‘re adding cores to an existing executor, so no need
      // to check memory and executor limits
//  不检查memory和executor的限制
      keepScheduling && enoughCores
    }
  }
 
 
  // Keep launching executors until no more workers can accommodate any
  // more executors, or if we have reached this application‘s limits
  var freeWorkers = (0 until numUsable).filter(canLaunchExecutor)
  while (freeWorkers.nonEmpty) {
    freeWorkers.foreach { pos =>
      var keepScheduling = true
      while (keepScheduling && canLaunchExecutor(pos)) {
        // 要分配的cores
        coresToAssign -= minCoresPerExecutor
 
        // 已分配的cores
        assignedCores(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.
        // 一个worker只启动一个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.
        // 如果没有开启spreadOut算法，就一直在一个worker上分配，直到不能在分配为止，
        // 这个算法的意思就是，每个Application，都尽可能分配到尽量少的worker上，比如总过有10个worker，每个有10个CPU core
        // 而我们的Application总共需要20个core， 那么其实 就只用到两个worker 
        if (spreadOutApps) {
          keepScheduling = false
        }
      }
    }
    freeWorkers = freeWorkers.filter(canLaunchExecutor)
  }
  assignedCores
}
 
 
代码3
//分配CPUcore的算法
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.
  // 需要的cores / 每个executor的cores 得到真正需要启动的executor数量
  val numExecutors = coresPerExecutor.map { assignedCores / _ }.getOrElse(1)
  val coresToAssign = coresPerExecutor.getOrElse(assignedCores)
  for (i <- 1 to numExecutors) {
 
    // 首先在Application内部缓存结构中，添加executors
    // 并且创建ExecutorDesc对象，其中封装了，给这个executor分配多少个CPU core
    // spark 1.3.0版本的executor启动的内部机制
    // 在spark-submit脚本中， 可以指定要多少个executor，每个executor多少个CPU，多少内存，那么基于我们的机制，实际上，最后，executor的实际数量， 以及每个executor的CPU， 可能与配置是不一样的。
    // 因为我们这里是基于总的CPU来分配的，就是说，比如要求3个executor，每个executor要3个CPU，那么
    // 当我们有9个worker，每个worker有1个CPU时，那么其实总共是要分配9个CPU core， 其实根据这种算法，会给每个worker分配一个CPU core， 然后给每个worker启动一个executor
    // 最后总过会启动9个executor ，每个executor有一个CPUcore
    // application  需要记录executor
    val exec = app.addExecutor(worker, coresToAssign)
 
    // 接着在worker上启动executor
    launchExecutor(worker, exec)// 详细代码见：代码4
 
    // 然后将Application的状态修改为RUNNING
    app.state = ApplicationState.RUNNING
  }
}
 
代码4
private def launchExecutor(worker: WorkerInfo, exec: ExecutorDesc): Unit = {
  logInfo("Launching executor " + exec.fullId + " on worker " + worker.id)
  
  // 将executor加入worker内部缓存中
  worker.addExecutor(exec)
 
  // 向worker发送LaunchExecutor消息
  worker.endpoint.send(LaunchExecutor(masterUrl,
    exec.application.id, exec.id, exec.application.desc, exec.cores, exec.memory))
 
  // 向executor对应的application的driver，发送executorAdded消息
  exec.application.driver.send(
    ExecutorAdded(exec.id, worker.id, worker.hostPort, exec.cores, exec.memory))
}