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MapReduce is one type of application that can run on the Hadoop 2.x framework. MapReduce configuration options are stored in the /opt/mapr/hadoop/hadoop-2.x.x/etc/hadoop/mapred-site.xml file and are editable by the root user. This file contains configuration information that overrides the default values for MapReduce parameters. Overrides of the default values for core configuration properties are stored in the Default mapred Parameters file.

To override a default value for a property, specify the new value within the <configuration> tags, using the following format:

Configurations for MapReduce Applications

mapreduce.framework.nameyarnExecution framework set to Hadoop YARN. resource limit for maps. heap-size for child jvms of maps.
mapreduce.reduce.memory.mb3072Larger resource limit for reduces. heap-size for child jvms of reduces. memory limit while sorting data for efficiency. streams merged at once while sorting files.
mapreduce.reduce.shuffle.parallelcopies50Higher number of parallel copies run by reduces to fetch outputs from very large number of maps.

Configurations for MapReduce JobHistory Server

mapreduce.jobhistory.addressMapReduce JobHistory Server host:portDefault port is 10020.
mapreduce.jobhistory.webapp.addressMapReduce JobHistory Server Web UI host:portDefault port is 19888.
mapreduce.jobhistory.intermediate-done-dir/mr-history/tmpDirectory where history files are written by MapReduce jobs.
mapreduce.jobhistory.done-dir/mr-history/doneDirectory where history files are managed by the MapReduce JobHistory Server.

Sample Hadoop 2.x mapred-site.xml File

The following mapred-site.xml file defines values for two job history parameters.

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