RDD中cache和persist的区别

通过观察RDD.scala源代码即可知道cache和persist的区别：

def persist(newLevel: StorageLevel): this.type = { 　　if (storageLevel != StorageLevel.NONE && newLevel != storageLevel) { 　　　　throw new UnsupportedOperationException( "Cannot change storage level of an RDD after it was already assigned a level") 　　} 　　sc.persistRDD(this) 　　sc.cleaner.foreach(_.registerRDDForCleanup(this)) 　　storageLevel = newLevel 　　this } /** Persist this RDD with the default storage level (`MEMORY_ONLY`). */ def persist(): this.type = persist(StorageLevel.MEMORY_ONLY)   /** Persist this RDD with the default storage level (`MEMORY_ONLY`). */ def cache(): this.type = persist()

 

 

 

 

 

 

 

 

 

 

 

可知：

1）RDD的cache()方法其实调用的就是persist方法，缓存策略均为MEMORY_ONLY；

2）可以通过persist方法手工设定StorageLevel来满足工程需要的存储级别；

3）cache或者persist并不是action；