RDD中cache和persist的區別

通過觀察RDD.scala源代碼即可知道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()

 

 

 

 

 

 

 

 

 

 

 

可知：

1）RDD的cache()方法其實調用的就是persist方法，緩存策略均為MEMORY_ONLY；

2）可以通過persist方法手工設定StorageLevel來滿足工程需要的存儲級別；

3）cache或者persist並不是action；