could not see the print out log in spark functions as mapPartitions

[Zhiliang Zhu]

Hi All,
I need debug spark job, my general way is to print out the log, however, some 
bug is in spark functions as mapPartitions etc, and not any log printed from 
those functionscould be found...Would you help point what is way to the log in 
the spark own function as mapPartitions? Or, what is general way to debug spark 
job.
Thank you in advance!
Zhiliang