spark 特殊函数时间:2023-03-09 16:27:03 private var seed: Long = System.nanoTime()//返回最准确的可用系统计时器的当前值,以毫微秒为单位 require(storageLevel != StorageLevel.NONE, "ALS is not designed to run without persisting intermediate RDDs.") 相当于c++ assert sc.defaultParallelism 默认的并行度是8