why the hadoop output file part-r-00000 is empty
Question 1 - read the counters:
Map input records=23
Map output records=0
Part-r-00000 is empty, because nothing is making it out of your map task. If you add the code of your map task to your post, we might be able to tell you why.
Question 2 - read the answers to this question, they might help you out.