Doubt in reducer

Hi, I am running a map reduce program which reads data from a file, processes it and writes the output into another file. i run 4 maps and 4 reduces, and my output is as follows: 09/08/27 17:34:37 INFO mapred.JobClient: Running job: job_200908271142_0026 09/08/27 17:34:38 INFO

Re: Doubt in reducer

But reducer can do some preparations during map process. It can distribute map output across nodes that will work as reducers. Copying and sorting map output is also time costuming process (maybe, more consuming than reduce itself). For example, piece job run log on 40node cluster could be