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https://issues.apache.org/jira/browse/MAPREDUCE-4613?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Vasco updated MAPREDUCE-4613:
-----------------------------
Description:
If a job has more reduce tasks than there are containers available, then the
reduce tasks can occupy all containers causing starvation. The attached graph
illustrates the behaviour. Scheduler used is fifo.
I understand that the correct behaviour when all containers are taken by
reducers while mappers are still pending, is for the running reducers to be
"pre-empted". However, pre-emption does not occur.
A work-around is to set the number of reducers < available containers.
was:
If a job has more reduce tasks than there are containers available, then the
reduce tasks can occupy all containers causing starvation.
I understand that the correct behaviour when all containers are taken by
reducers while mappers are still pending, is for the running reducers to be
"pre-empted". However, pre-emption does not occur.
A work-around is to set the number of reducers < available containers.
> Scheduling of reduce tasks results in starvation
> ------------------------------------------------
>
> Key: MAPREDUCE-4613
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4613
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: scheduler
> Affects Versions: 0.23.1, 2.0.1-alpha
> Environment: 16 machine cluster
> Reporter: Vasco
> Attachments: scheduling.png
>
>
> If a job has more reduce tasks than there are containers available, then the
> reduce tasks can occupy all containers causing starvation. The attached graph
> illustrates the behaviour. Scheduler used is fifo.
> I understand that the correct behaviour when all containers are taken by
> reducers while mappers are still pending, is for the running reducers to be
> "pre-empted". However, pre-emption does not occur.
> A work-around is to set the number of reducers < available containers.
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