记录读取器的概念

Question

We know that prior to Mapper phase the files are split and the RecordReader starts working to emit a input to the Mapper. My question is whether the reducer uses a RecordReader class to read the data emitted by the mapper?

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because reducer takes input too!! Please Explain!!!

Answer 1

Overview of the mapreduce steps is as follows

1) InputFormat :

 - Validates the Input.

 - Splits the input files.        

 - Gives Record Reader Implementation to give input to Mapper.

2)Mapper Phase

3)Shuffle and Sort Phase

4)Reducer Phase

5) OutputFormat     

 - Validates the Output Specification.  

 - Provides Record Writer Implementation used to write the output files.

Reducer does not use record reader...