RDD 5大特性在源码中的体现

最新推荐文章于 2024-10-15 16:03:42 发布

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本文深入探讨了RDD（弹性分布式数据集）的五大核心特性，包括如何计算分区、返回依赖关系、指定位置偏好、分区策略及获取分区集合。通过详细解析这些特性，读者将对RDD的工作原理有更深刻的理解。

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  /**
   * :: DeveloperApi ::
   * Implemented by subclasses to compute a given partition.
   */
def compute(split: Partition, context: TaskContext): Iterator[T]

对应 RDD特点二

**
   * Implemented by subclasses to return the set of partitions in this RDD. This method will only
   * be called once, so it is safe to implement a time-consuming computation in it.
   *
   * The partitions in this array must satisfy the following property:
   *   `rdd.partitions.zipWithIndex.forall { case (partition, index) => partition.index == index }`
   */
protected def getPartitions: Array[Partition]

对应RDD特点一

  /**
   * Implemented by subclasses to return how this RDD depends on parent RDDs. This method will only
   * be called once, so it is safe to implement a time-consuming computation in it.
   */
protected def getDependencies: Seq[Dependency[_]] = deps

对应RDD特点三

 /**
   * Optionally overridden by subclasses to specify placement preferences.
   */
protected def getPreferredLocations(split: Partition): Seq[String] = Nil

对应特点五

 /** Optionally overridden by subclasses to specify how they are partitioned. */
@transient val partitioner: Option[Partitioner] = None

对应特点四

RDD 5大特性 在源码中的体现

RDD 5大特性在源码中的体现