Introducing MRv1 and MRv2

The MapReduce framework in Hadoop 1.x version is also known as MRv1. The MRv1 framework includes client communication, job execution and management, resource scheduling and resource management. The Hadoop daemons associated with MRv1 are JobTracker and TaskTracker as shown in the following figure:

JobTracker is a master service responsible for client communications, MapReduce job management, scheduling, resource management, and so on. The TaskTracker service is a worker daemon that runs on every slave of the Hadoop cluster. It is responsible for the execution of map reduce tasks. A client submits a job to the JobTracker service. The JobTracker validates the request and breaks the job into tasks. The JobTracker uses a data localization mechanism and assigns TaskTracker for the execution of tasks. The TaskTracker service runs a map reduce task as a separate JVM named as child as described in the following figure:

The following diagram shows the MRv1 services and...