MapR 5.0 Documentation : TaskTracker on CLDB or ZooKeeper Nodes

If running the TaskTracker on CLDB or ZooKeeper nodes is unavoidable, certain settings in mapred-site.xml should be configured differently to protect critical cluster-wide services from resource shortages. In particular, the number of slots advertised by the TaskTracker should be reduced and less memory should be reserved for MapReduce tasks. Edit /opt/mapr/hadoop/hadoop-<version>/conf/mapred-site.xml and set the following parameters:

mapred.tasktracker.map.tasks.maximum=(CPUS > 2) ? (CPUS * 0.50) : 1
mapred.tasktracker.reduce.tasks.maximum=(CPUS > 2) ? (CPUS * 0.25) : 1
mapreduce.tasktracker.prefetch.maptasks=0.25
mapreduce.tasktracker.reserved.physicalmemory.mb.low=0.50
mapreduce.tasktracker.task.slowlaunch=true