Combiner also known as Mini-Reducer acts as an optional step between Map and Reduce. Briefly we can that, it helps to take the output from Map function. It then summarizes that output using the same key and then it passes the final summarized records as input to the Reducer. When we make use of MapReduce job on a large dataset. Then large chunk of data is generated by the Mapper which when passed to the reducer for further processing can cause congestion in the network. In order to deal with kind of congestion, Combiner is used by Hadoop Framework as an intermediate between Mapper and Reducer to reduce network congestion.