RDD的5大特性

RDD5大特点

 * Internally, each RDD is characterized by five main properties:
 *
 *  - A list of partitions
 *  - A function for computing each split
 *  - A list of dependencies on other RDDs
 *  - Optionally, a Partitioner for key-value RDDs (e.g. to say that the RDD is hash-partitioned)
 *  - Optionally, a list of preferred locations to compute each split on (e.g. block locations for
 *    an HDFS file)

特点一

A list of partitions

RDD的基本构成是有partitions构成的,

特点二

A function for computing each split

对每个分区都是用相通的函数记性计算

特点三

A list of dependencies on other RDDs

• RDD之间是有依赖关系的;
  • RDDA==>RDDB==>RDDC==>RDDD
• 这几个RDD之间都是有相互依赖的关系,**假设RDDC数据丢失了,可以让RDDB重新计算给RDDC,**这就是RDD弹性的体现,

特点四

Optionally, a Partitioner for key-value RDDs (e.g. to say that the RDD is hash-partitioned)

分区的时候,默认是对key做hash 进行分发

特点五

 Optionally, a list of preferred locations to compute each split on (e.g. block locations for an HDFS file

数据本地化计算,数据在哪里我们的计算的task就应该在哪里计算,这样性能最好

RDD的5个特性,都体现出来了RDD(Resilient Distributed Dataset )