RDD中cache和persist的區別

 

RDD中cache和persist的區別

  

 

經過觀察RDD.scala源代碼便可知道cache和persist的區別：

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()