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package spark
/**
* Base class for dependencies.
*/
abstract class Dependency[T](val rdd: RDD[T]) extends Serializable
/**
* Base class for dependencies where each partition of the parent RDD is used by at most one
* partition of the child RDD. Narrow dependencies allow for pipelined execution.
*/
abstract class NarrowDependency[T](rdd: RDD[T]) extends Dependency(rdd) {
/**
* Get the parent partitions for a child partition.
* @param outputPartition a partition of the child RDD
* @return the partitions of the parent RDD that the child partition depends upon
*/
def getParents(outputPartition: Int): Seq[Int]
}
/**
* Represents a dependency on the output of a shuffle stage.
* @param shuffleId the shuffle id
* @param rdd the parent RDD
* @param partitioner partitioner used to partition the shuffle output
*/
class ShuffleDependency[K, V](
@transient rdd: RDD[(K, V)],
val partitioner: Partitioner)
extends Dependency(rdd) {
val shuffleId: Int = rdd.context.newShuffleId()
}
/**
* Represents a one-to-one dependency between partitions of the parent and child RDDs.
*/
class OneToOneDependency[T](rdd: RDD[T]) extends NarrowDependency[T](rdd) {
override def getParents(partitionId: Int) = List(partitionId)
}
/**
* Represents a one-to-one dependency between ranges of partitions in the parent and child RDDs.
* @param rdd the parent RDD
* @param inStart the start of the range in the parent RDD
* @param outStart the start of the range in the child RDD
* @param length the length of the range
*/
class RangeDependency[T](rdd: RDD[T], inStart: Int, outStart: Int, length: Int)
extends NarrowDependency[T](rdd) {
override def getParents(partitionId: Int) = {
if (partitionId >= outStart && partitionId < outStart + length) {
List(partitionId - outStart + inStart)
} else {
Nil
}
}
}
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