I ask this issue under the spark discussion group, and has some reply。
https://lists.apache.org/thread.html/rae7cc9057c3e90f439de5b899d0b0c0fb1e9cbee85349d15ec1236e9%40%3Cdev.spark.apache.org%3EThis is a good phenomenon, although looking at this reply is very academic.
Let's talk more about the driver.