spark 特殊函数

原文链接： http://www.cnblogs.com/ChenAlong/p/5458586.html

• 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

转载于:https://www.cnblogs.com/ChenAlong/p/5458586.html