Spark动态资源分配的资源释放过程及BlockManager清理过程

Spark动态资源分配过程中YarnScheduler 释放资源过程

SchedulerBackend， TaskScheduler 和 ExecutorAllocationManager 的创建

val (_schedulerBackend, _taskScheduler) = SparkContext.createTaskScheduler( sc: SparkContext, master: String, deployMode: String): (SchedulerBackend, TaskScheduler)– 根据给定的master URL创建一个task scheduler

通过ServiceLoader.load(classOf[ExternalClusterManager], loader).asScala.filter(_.canCreate(url))服务加载所有注册的ExternalClusterManager,参考 META-INF/services 目录下的org.apache.spark.scheduler.ExternalClusterManager文件，这里注册了YarnClusterManager，且通过canCreate(url) 方法返回唯一的Yarn调度器。

org.apache.spark.scheduler.ExternalClusterManager
  org.apache.spark.scheduler.cluster.YarnClusterManager

通过 YarnClusterManager 生成的_schedulerBackend = YarnClusterSchedulerBackend， scheduler = YarnScheduler。YarnClusterSchedulerBackend 和 YarnScheduler类继承关系如下:

YarnClientSchedulerBackend
  YarnSchedulerBackend : Yarn的资源管理事件都在这里， RegisterClusterManager, RemoveExecutor, RequestExecutors, KillExecutors等
    CoarseGrainedSchedulerBackend
      ExecutorAllocationClient

YarnScheduler
  TaskSchedulerImpl
    TaskScheduler

SparkContext 在初始化的时候如果开启动态资源分配，会实例化一个 ExecutorAllocationManager() 并start。在ExecutorAllocationManager内部会调用上面的YarnClusterSchedulerBackend（就是后面的client）来进行实际的调度。

_executorAllocationManager = Some(new ExecutorAllocationManager(schedulerBackend.asInstanceOf[ExecutorAllocationClient], listenerBus, _conf, cleaner = cleaner))

ExecutorAllocationManager

ExecutorAllocationManager 服务起来后会启动一个后台线程循环调度，executorMonitor 会把超时的Executor list去取出来，并调用 removeExecutors()进行executor资源释放。

def start(): Unit
  def schedule(): Unit
    val executorIdsToBeRemoved = executorMonitor.timedOutExecutors()
    def removeExecutors(executors: Seq[String])
      client.killExecutors(executorIdsToBeRemoved, adjustTargetNumExecutors = false, countFailures = false, force = false)

上面调用client: ExecutorAllocationClient的killExecutors方法。client实际上就是我们之前看到的class CoarseGrainedSchedulerBackend extends ExecutorAllocationClient

CoarseGrainedSchedulerBackend

def killExecutors()
doKillExecutors(executorsToKill)
  YarnSchedulerBackend: 
    def doKillExecutors(executorIds: Seq[String])
    yarnSchedulerEndpointRef.ask[Boolean](KillExecutors(executorIds))

o.a.s.scheduler.cluster.YarnSchedulerEndpoint

YarnSchedulerEndpoint 直接将 KillExecutors 的请求转发给 AMEndpoint var amEndpoint: Option[RpcEndpointRef]

o.a.s.deploy.yarn.ApplicationMaster

ApplicationMaster 开始处理 KillExecutors 事件

case KillExecutors(executorIds) 
  YarnAllocator: 
  def killExecutor(executorId: String)
  internalReleaseContainer(container)
  amClient.releaseAssignedContainer(container.getId()) -- 主动向RM申请释放资源

BlockManager 清理Broadcast过程

BlockManager 管理的相关Relaition

SparkEnv
 - BlockManager
    - blockManagerMaster : 内部有两个EndpointRef,分别用于处理BlockManagerInfo 的 RPC事件和心跳事件， 管理 BlockManagerInfo 列表.  
      - driverEndpoint: BlockManagerMasterEndpoint : 为了管理所有BlockManagerInfo 内部维护了一个 blockManagerInfo: Map[BlockManagerId, BlockManagerInfo]
        - BlockManagerId 可以理解为由 executorId, host, port, topologyInfo 四个字段组成的一个标识符
        - BlockManagerInfo : 在Driver和Executor上都有，内部维护当前有的 blocks: JHashMap[BlockId, BlockStatus]信息，用于内存管理。当removeBlock时，会做标记删除，但是使用的进程内存 _remainingMem 不释放。
      - driverHeartbeatEndPoint: BlockManagerMasterHeartbeatEndpoint 日常心跳管理，忽略

val DRIVER_ENDPOINT_NAME = "BlockManagerMaster"
val DRIVER_HEARTBEAT_ENDPOINT_NAME = "BlockManagerMasterHeartbeat"

## Executor 端BlockManager的初始化和注册

BlockManagerInfo 在 Executor 实例化的时候通过发送 `RegisterBlockManager` 事件到 Driver Endpoint 进行注册

```java
CoarseGrainedExecutorBackend
EVENT: case RegisteredExecutor =>
  executor = new Executor(executorId, hostname, env, userClassPath, isLocal = false, resources = _resources)

Executor() 构造方法
  env.blockManager.initialize(conf.getAppId)  
    val id = BlockManagerId(executorId, blockTransferService.hostName, blockTransferService.port, None)
    val idFromMaster = master.registerBlockManager(id, ...* )
      val updatedId = driverEndpoint.askSync[BlockManagerId](RegisterBlockManager(id, localDirs, maxOnHeapMemSize, maxOffHeapMemSize, slaveEndpoint)) -- 向 driverEndpoint 发送注册事件

RemoveBroadcast 管理

当我们需要对集群Block进行管理的时候，只需要调用BlockManager中的master引用即可。例如：SparkEnv.get.blockManager.master.removeBroadcast(id, removeFromDriver, blocking)

BlockManagerMaster:
def removeBroadcast(broadcastId: Long, removeFromMaster: Boolean, blocking: Boolean): Unit -- master对象只是接口，将实际请求转给 driverEndpoint
val future = driverEndpoint.askSync[Future[Seq[Int]]](RemoveBroadcast(broadcastId, removeFromMaster))


driverEndpoint: BlockManagerMasterEndpoint
def removeBroadcast(broadcastId: Long, removeFromDriver: Boolean)
  -- 开始构造 新的RemoveBroadcast 事件，由Driver发送到各个Executor上的BlockManager
  val removeMsg = RemoveBroadcast(broadcastId, removeFromDriver)
  requiredBlockManagers.map {
     bm => bm.slaveEndpoint.ask[Int](removeMsg) }  

实际代码举例

val bcNewCenters = data.context.broadcast(newCenters) -- 创建broadcast对象

bcNewCenters.unpersist() --调用unpersist() 方法
Broadcast.scala
def unpersist(): Unit
def unpersist(blocking: Boolean): Unit
TorrentBroadcast.scala : def doUnpersist(blocking: Boolean): Unit
def unpersist(id: Long, removeFromDriver: Boolean, blocking: Boolean): Unit
SparkEnv.get.blockManager.master.removeBroadcast(id, removeFromDriver, blocking)