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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；