[jira] [Created] (YARN-6191) CapacityScheduler preemption by container priority can be problematic for MapReduce

["Jason Lowe (JIRA)" <ji...@apache.org>]

Jason Lowe created YARN-6191:
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             Summary: CapacityScheduler preemption by container priority can be problematic for MapReduce
                 Key: YARN-6191
                 URL: https://issues.apache.org/jira/browse/YARN-6191
             Project: Hadoop YARN
          Issue Type: Bug
          Components: capacityscheduler
            Reporter: Jason Lowe


A MapReduce job with thousands of reducers and just a couple of maps left to go was running in a preemptable queue.  Periodically other queues would get busy and the RM would preempt some resources from the job, but it _always_ picked the job's map tasks first because they use the lowest priority containers.  Even though the reducers had a shorter running time, most were spared but the maps were always shot.  Since the map tasks ran for a longer time than the preemption period, the job was in a perpetual preemption loop.



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