Customizing the MapReduce v1 Slot Calculation Parameters

In general, you should not need to customize the number of map and reduce slots because Warden determines these value based on the resource available on the node. However, you can override the number of slots by adding one or more of these parameters to mapred-site.xml. The mapred-site.xml file for MapReduce v1 jobs is in the following location: /opt/mapr/hadoop/hadoop-0.20.2/conf/mapred-site.xml.

Note: If you make changes to mapred-site.xml, you must restart TaskTracker.
Warden uses the following parameters to calculate and assign values to map slots and reduce slots on each node:
Parameter Default Value Description
mapreduce.tasktracker.reserved.physicalmemory.mb Warden uses the following formula to calculate this value:
[total physical memory on node] – 
[memory required by the operating system, MapR file system and MapR services installed on the node]-
[memory allocated to YARN applications, if Node Manager is installed on the node]
For more information, see Memory Allocation for Nodes. To determine the value, go to the TaskTracker UI and view the memory available for that node.
Defines the memory available to process MapReduce v1 tasks in MB.
mapred.tasktracker.map.tasks.maximum Warden uses a formula to calculate this value. For more information, see Criteria for Map Slot Calculation. Defines the maximum number of MapReduce v1 map slots.
mapred.tasktracker.reduce.tasks.maximum Warden uses a formula to calculate this value. For more information, see Criteria for Reduce Slot Calculation. Defines the maximum number of MapReduce v1 map slots.
mapred.job.map.memory.physical.mb If the chunk size is greater than or equal to 256M, then this value is set to 1G. Otherwise, this value is set to 0.5G. For information about configuring the chunk size, see Chunk Size. Defines the amount of memory allocated to map tasks in MB.
mapred.job.reduce.memory.physical.mb If the chunk size is greater than or equal to 256M, then this value is set to 3G. Otherwise, this value is set to 1.5G. For information about configuring the chunk size, see Chunk Size. Defines the amount of memory allocated to reduce tasks in MB.