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HADOOP - What Mapper does?

asked SRVMTrainings December 13, 2012 06:29 AM  

What Mapper does?


2 Answers

answered By   0  

Mapper reads a file line by line (streaming) way and takes the byte offset of each line as key and the whole line as value and define it as pairs. It passes these key value pairs to the intermediate step before a Mapper starts processing the key value pairs
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answered By rajaniikanth   0  

"Map" step: The master node takes the input, divides it into smaller sub-problems, and distributes them to worker nodes. A worker node may do this again in turn, leading to a multi-level tree structure. The worker node processes the smaller problem, and passes the answer back to its master node.

"Reduce" step: The master node then collects the answers to all the sub-problems and combines them in some way to form the output – the answer to the problem it was originally trying to solve.

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