hadoop: difference between 0 reducer and identity reducer?

Question

I am just trying to confirm my understanding of difference between 0 reducer and identity reducer.

• 0 reducer means reduce step will be skipped and mapper outp

Answer 1

Another use-case for using the Identity Reducer is to combine all the results into <# of reducers> output files. This can be handy if you are using Amazon Web Services to write to S3 directly, especially if the mapper output is small (e.g. a grep/search for a record), and you have a lot of mappers (e.g. 1000's).