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
