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Can anyone tell me what is reducer in Hadoop?

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Reducer is the second phase of processing in Hadoop which comes after Mapper phase. Reducer takes the output of the mapper as the input and processes and produces a new set of output, which will be stored in the HDFS.

Reducer first processes the intermediate values for a particular key generated by the map function and then generates the output (zero or more key-value pair).

The user decides the number of reducers. By default, the number of reducers is 1.

If you want to learn Hadoop, I recommend this Hadoop Certification program by Intellipaat.

Also, watch this YouTube tutorial on Hadoop:

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