In Hadoop, the primary phases of reducer are as follows: Shuffle: In this phase, the mapper’s sorted output becomes the input to the reducer. Sort: In this phase, Hadoop sorts the input to Reducer using the same key. Both the Sort and Shuffle phases happen concurrently. Reduce: This phase occurs after the sort and shuffle phase. In this phase, output values associated with a specific key are reduced to consolidate the data into the reducer final output. Reducer output sorting is not there.