About Apache Hadoop MapReduce Version 1 (MRv1) and Version 2 (MRv2)

  Important: Cloudera recommends that you use YARN (now production-ready) with CDH 5.

• MapReduce 2.0 (MRv2): CDH 5 includes MapReduce 2.0 (MRv2) running on YARN. The fundamental idea of the YARN architecture is to split up the two primary responsibilities of the JobTracker — resource management and job scheduling/monitoring — into separate daemons: a global ResourceManager (RM) and per-application ApplicationMasters (AM). With MRv2, the ResourceManager (RM) and per-node NodeManagers (NM), form the data-computation framework. The ResourceManager service effectively replaces the functions of the JobTracker, and NodeManagers run on slave nodes instead of TaskTracker daemons. The per-application ApplicationMaster is, in effect, a framework-specific library and is tasked with negotiating resources from the ResourceManager and working with the NodeManager(s) to execute and monitor the tasks. For details of the new architecture, see Apache Hadoop NextGen MapReduce (YARN).

• MapReduce Version 1 (MRv1): For backward compatibility, CDH 5 continues to support the original MapReduce framework (i.e. the JobTracker and TaskTrackers), but you should begin migrating to MRv2.
    Note:

  Cloudera does not support running MRv1 and YARN daemons on the same nodes at the same time.

• Deprecated properties:
  In Hadoop 2.0.0 and later (MRv2), a number of Hadoop and HDFS properties have been deprecated. (The change dates from Hadoop 0.23.1, on which the Beta releases of CDH 4 were based). A list of deprecated properties and their replacements can be found at Hadoop Deprecated Properties.

    Note: All of these deprecated properties continue to work in MRv1. Conversely the new mapreduce* properties listed do not work in MRv1.