DAG(Directed Acyclic Graph)有向无环图是由点和线组成的拓扑图形,该图形具有方向,不会闭环。例如,DAG 记录了 RDD 的转换过程和任务的阶段。
Application:初始化一个 SparkContext 即生成一个 Application;
Job:一个 Action 算子就会生成一个 Job;
Stage:Stage 等于宽依赖(ShuffleDependency)的个数加 1;
Task:一个 Stage 阶段中,最后一个 RDD 的分区个数就是 Task 的个数。
val tasks: Seq[Task[_]] = try { stage match { case stage: ShuffleMapStage => partitionsToCompute.map { id => val locs = taskIdToLocations(id) val part = stage.rdd.partitions(id) new ShuffleMapTask(stage.id, stage.latestInfo.attemptId, taskBinary, part, locs, stage.latestInfo.taskMetrics, properties, Option(jobId), Option(sc.applicationId), sc.applicationAttemptId) } case stage: ResultStage => partitionsToCompute.map { id => val p: Int = stage.partitions(id) val part = stage.rdd.partitions(p) val locs = taskIdToLocations(id) new ResultTask(stage.id, stage.latestInfo.attemptId, taskBinary, part, locs, id, properties, stage.latestInfo.taskMetrics, Option(jobId), Option(sc.applicationId), sc.applicationAttemptId) } }
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