In this section, we briefly describe major features of MR3.
One can try these features by changing corresponding configurations in
mr3-site.xml in the classpath.
We assume some familiarity with such notions as DAG, Vertex, Task, and TaskAttempt.
For clarity, we refer to client program in MR3 as MR3Client, ApplicationMaster in MR3 as DAGAppMaster, and container in MR3 as ContainerWorker.