Spark FinalStage处理(Stage划分)

更多资源

• github: https://github.com/opensourceteams/spark-scala-maven
• csdn(汇总视频在线看): https://blog.csdn.net/thinktothings/article/details/84726769

Youtube视频

• Spark FinalStage处理(Stage划分)(Youtube视频) : https://youtu.be/yFJugOV0Fak

BiliBili视频

• Spark FinalStage处理(Stage划分)(bilibili视频) : https://www.bilibili.com/video/av37445057/

说明

• 由于DAGScheduler进行stage提交传的参数为FinalStage,所以对FinalStage的构成进行分析
• RDD依赖为shuffleDep的stage已经进行了缓存,(这个时候已经对Stage进行明显的划分，只是没有提交) shuffleToMapStage.get(shuffleDep.shuffleId)

DAGScheduler事件处理JobSubmitted

• 调用newResultStage()方法

private[scheduler] def handleJobSubmitted(jobId: Int,
      finalRDD: RDD[_],
      func: (TaskContext, Iterator[_]) => _,
      partitions: Array[Int],
      callSite: CallSite,
      listener: JobListener,
      properties: Properties) {
    var finalStage: ResultStage = null
    try {
      // New stage creation may throw an exception if, for example, jobs are run on a
      // HadoopRDD whose underlying HDFS files have been deleted.
      finalStage = newResultStage(finalRDD, func, partitions, jobId, callSite)
    } catch {
      case e: Exception =>
        logWarning("Creating new stage failed due to exception - job: " + jobId, e)
        listener.jobFailed(e)
        return
    }

    val job = new ActiveJob(jobId, finalStage, callSite, listener, properties)
    clearCacheLocs()
    logInfo("Got job %s (%s) with %d output partitions".format(
      job.jobId, callSite.shortForm, partitions.length))
    logInfo("Final stage: " + finalStage + " (" + finalStage.name + ")")
    logInfo("Parents of final stage: " + finalStage.parents)
    logInfo("Missing parents: " + getMissingParentStages(finalStage))

    val jobSubmissionTime = clock.getTimeMillis()
    jobIdToActiveJob(jobId) = job
    activeJobs += job
    finalStage.setActiveJob(job)
    val stageIds = jobIdToStageIds(jobId).toArray
    val stageInfos = stageIds.flatMap(id => stageIdToStage.get(id).map(_.latestInfo))
    listenerBus.post(
      SparkListenerJobStart(job.jobId, jobSubmissionTime, stageInfos, properties))
    submitStage(finalStage)

    submitWaitingStages()
  }

• 调用方法getParentStagesAndId()得到上级stage列表

  /**
   * Create a ResultStage associated with the provided jobId.
   */
  private def newResultStage(
      rdd: RDD[_],
      func: (TaskContext, Iterator[_]) => _,
      partitions: Array[Int],
      jobId: Int,
      callSite: CallSite): ResultStage = {
    val (parentStages: List[Stage], id: Int) = getParentStagesAndId(rdd, jobId)
    val stage = new ResultStage(id, rdd, func, partitions, parentStages, jobId, callSite)
    stageIdToStage(id) = stage
    updateJobIdStageIdMaps(jobId, stage)
    stage
  }

• 调用方法getParentStages()

  /**
   * Helper function to eliminate some code re-use when creating new stages.
   */
  private def getParentStagesAndId(rdd: RDD[_], firstJobId: Int): (List[Stage], Int) = {
    val parentStages = getParentStages(rdd, firstJobId)
    val id = nextStageId.getAndIncrement()
    (parentStages, id)
  }

• 该方法计算上级stage
• 根据当前RDD=rdd4 的依赖类型判断是不是ShuffleDependency
• 不是，找上级RDD，再继续判断上级RDD的依赖类型
• 是，创建ShuffleMapStage并还回，此stage的RDD为rdd4的上级RDD
• 注意只要有上级stage,就会一直先找上级stage,这样找到根上的stage的id为0,依次子stage的id加1

/**
   * Get or create the list of parent stages for a given RDD.  The new Stages will be created with
   * the provided firstJobId.
   */
  private def getParentStages(rdd: RDD[_], firstJobId: Int): List[Stage] = {
    val parents = new HashSet[Stage]
    val visited = new HashSet[RDD[_]]
    // We are manually maintaining a stack here to prevent StackOverflowError
    // caused by recursively visiting
    val waitingForVisit = new Stack[RDD[_]]
    def visit(r: RDD[_]) {
      if (!visited(r)) {
        visited += r
        // Kind of ugly: need to register RDDs with the cache here since
        // we can't do it in its constructor because # of partitions is unknown
        for (dep <- r.dependencies) {
          dep match {
            case shufDep: ShuffleDependency[_, _, _] =>
              parents += getShuffleMapStage(shufDep, firstJobId)
            case _ =>
              waitingForVisit.push(dep.rdd)
          }
        }
      }
    }
    waitingForVisit.push(rdd)
    while (waitingForVisit.nonEmpty) {
      visit(waitingForVisit.pop())
    }
    parents.toList
  }

图解FinalStage