DAG
https://blog.csdn.net/qq_16669583/article/details/106026722
https://blog.csdn.net/u011564172/article/details/70172060
作用
根据rdd的依赖关系构建dag，然后基于dag划分stage
https://blog.csdn.net/qq_16669583/article/details/106026722
https://blog.csdn.net/u011564172/article/details/70172060
根据rdd的依赖关系构建dag，然后基于dag划分stage