I have about 170 GB data. I have to analyze it using hadoop 2.7.3. There are 14 workers. I have to find total of unique MIME type of each document e.g. total number of documents that are text/html type. When I run mapreduce job(written in python), Hadoop returns many output files instead of single one that I am expecting. I think this is due to many workers that process some data seprately and give output. I want to get single output. Where is the problem. How I can restrict hadoop to give single output (by combining all small output files).
your job is generating 1 file per mapper, you have to force a reducer phase using 1 reducer to do this, you can accomplish this  emitting the same key in all the mappers.
How to combine hadoop mappers output to get single result