Add new Counters to MapReduce Source

[#1]

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I want to measure the time taken by the MapReduce framework to read data from HDFS using counters. The current counters don't include that. I have looked at the MapReduce source code on Github but I am still unable to wrap my head around the whole flow. Looking at the source, I think read operation is done from the below java class and nextKeyValue() method.

org/apache/hadoop/mapreduce/lib/input/LineRecordReader.java 

I know I can have an empty Mapper approach to do this but since I will be running lot of experiments then that will not be very ideal.

Any pointers is highly appreciated.

[#2]

@Neeraj Sabharwal any ideas or pointers here?