Jason Lowe created MAPREDUCE-4228:
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Summary: mapreduce.job.reduce.slowstart.completedmaps is not working properly
to delay the scheduling of the reduce tasks
Key: MAPREDUCE-4228
URL: https://issues.apache.org/jira/browse/MAPREDUCE-4228
Project: Hadoop Map/Reduce
Issue Type: Bug
Components: applicationmaster, mrv2
Affects Versions: 0.23.1
Reporter: Jason Lowe
Assignee: Jason Lowe
If no more map tasks need to be scheduled but not all have completed, the ApplicationMaster
will start scheduling reducers even if the number of completed maps has not met the mapreduce.job.reduce.slowstart.completedmaps
threshold. For example, if the property is set to 1.0 all maps should complete before any
reducers are scheduled. However the reducers are scheduled as soon as the last map task is
assigned to a container. For a job with very long-running maps, a cluster with enough capacity
to launch all map tasks could cause reducers to launch prematurely and waste cluster resources.
Thanks to Phil Su for discovering this issue.
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