Spark DAG的生成
https://www.pianshen.com/article/84211071565/
spark学习(二)RDD和DAG
https://blog.csdn.net/weixin_40535323/article/details/82874525
spark中的RDD以及DAG
https://www.cnblogs.com/wnbahmbb/p/6271375.html
Spark中RDD的运行机制
https://www.pianshen.com/article/69071210354/