问题
I am trying to write some performance-mindful code in Spark and wondering whether I should write an Aggregator or a User-defined Aggregate Function (UDAF) for my rollup operations on a Dataframe.
I have not been able to find any data anywhere on how fast each of these methods are and which you should be using for spark 2.0+.
来源：https://stackoverflow.com/questions/45356452/performance-of-udaf-versus-aggregator-in-spark