Chapter 3. Understanding MapReduce
The previous two chapters have discussed the problems that Hadoop allows us to solve, and gave some hands-on experience of running example MapReduce jobs. With this foundation, we will now go a little deeper.
In this chapter we will be:
- Understanding how key/value pairs are the basis of Hadoop tasks
- Learning the various stages of a MapReduce job
- Examining the workings of the map, reduce, and optional combined stages in detail
- Looking at the Java API for Hadoop and use it to develop some simple MapReduce jobs
- Learning about Hadoop input and output
Key/value pairs
Since Chapter 1, What It's All About, we have been talking about operations that process and provide the output in terms of key/value pairs without explaining ...
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