Caching

[Amit Sharma]

Hi All, I am using caching in my code. I have a DF like
val  DF1 = read csv.
val DF2 = DF1.groupBy().agg().select(.....)

Val DF3 =  read csv .join(DF1).join(DF2)
  DF3 .save.

If I do not cache DF2 or Df1 it is taking longer time  . But i am doing 1
action only why do I need to cache.

Thanks
Amit