CDH 5 and MapReduce
CDH 5 supports two versions of the MapReduce computation framework: MRv1 and MRv2. The default installation in CDH 5 is MapReduce (MRv2) built on the YARN framework. In this document, Cloudera refers to MapReduce (MRv2) as YARN. You can use the instructions later in this section to install MRv1, YARN, or both implementations.
The MapReduce v2 (MRv2) or YARN architecture splits the two primary responsibilities of the JobTracker — resource management and job scheduling/monitoring — into separate daemons: a global ResourceManager and per-application ApplicationMasters. With YARN, the ResourceManager and per-host NodeManagers form the data-computation framework. The ResourceManager service effectively replaces the functions of the JobTracker, and NodeManagers run on worker hosts instead of TaskTracker daemons. The per-application ApplicationMaster is, in effect, a framework-specific library and negotiates resources from the ResourceManager and works with the NodeManagers to run and monitor the tasks. For details of this architecture, see Apache Hadoop NextGen MapReduce (YARN).