Configuring the Fair Scheduler

The Fair Scheduler lets all applications run by default, but you can also limit the number of running applications per user and per queue through the configuration file. This can be useful when a user must submit hundreds of applications at once, or in general to improve performance if running too many applications at once would cause too much intermediate data to be created or too much context-switching. Limiting the applications does not cause any subsequently submitted applications to fail; it only causes them to wait in the scheduler's queue until earlier applications finish.

To customize the Fair Scheduler, set the configuration properties in yarn-site.xml and update the allocation file to list existing queues and their respective weights and capacities. The allocation file is automatically created during MapR installation, The default location for this file is:
{$MAPR_HOME}/hadoop/hadoop-2.x/etc/hadoop/fair-scheduler.xml

The file is reloaded every 10 seconds to refresh the scheduler with any modified settings that are specified in the file.