关于spark shuffle过程的理解:https://blog.youkuaiyun.com/quitozang/article/details/80904040
spark基础之shuffle机制和原理分析:https://blog.youkuaiyun.com/zhanglh046/article/details/78360762
Spark shuffle流程细则:https://blog.youkuaiyun.com/u014434646/article/details/79518973