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Stage

Stage is an abstraction of steps in a physical execution plan.

Note

The logical DAG or logical execution plan is the RDD lineage.

Indirectly, a Stage is a set of parallel tasks - one task per partition (of an RDD that computes partial results of a function executed as part of a Spark job).

Stage, tasks and submitting a job

In other words, a Spark job is a computation "sliced" (not to use the reserved term partitioned) into stages.

Contract

Missing Partitions

findMissingPartitions(): Seq[Int]

Missing partitions (IDs of the partitions of the RDD that are missing and need to be computed)

Used when:

Implementations

Creating Instance

Stage takes the following to be created:

  • Stage ID
  • RDD
  • Number of tasks
  • Parent Stages
  • First Job ID
  • CallSite
  • Resource Profile ID

Abstract Class

Stage is an abstract class and cannot be created directly. It is created indirectly for the concrete Stages.

RDD

Stage is given a RDD when created.

Stage ID

Stage is given an unique ID when created.

Note

DAGScheduler uses nextStageId internal counter to track the number of stage submissions.

Making New Stage Attempt

makeNewStageAttempt(
  numPartitionsToCompute: Int,
  taskLocalityPreferences: Seq[Seq[TaskLocation]] = Seq.empty): Unit

makeNewStageAttempt creates a new TaskMetrics and requests it to register itself with the SparkContext of the RDD.

makeNewStageAttempt creates a StageInfo from this Stage (and the nextAttemptId). This StageInfo is saved in the _latestInfo internal registry.

In the end, makeNewStageAttempt increments the nextAttemptId internal counter.

Note

makeNewStageAttempt returns Unit (nothing) and its purpose is to update the latest StageInfo internal registry.

makeNewStageAttempt is used when:

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