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https://issues.apache.org/jira/browse/MAPREDUCE-2729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13081118#comment-13081118
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Thomas Graves commented on MAPREDUCE-2729:
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The patch is for the branch-0.20-security branch. I will look at putting it on
trunk.
> Reducers are always counted having "pending tasks" even if they can't be
> scheduled yet because not enough of their mappers have completed
> -----------------------------------------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-2729
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2729
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Affects Versions: 0.20.205.0
> Environment: 0.20.1xx-Secondary
> Reporter: Sherry Chen
> Assignee: Sherry Chen
> Fix For: 0.20.205.0
>
> Attachments: MAPREDUCE-2729.patch
>
>
> In capacity scheduler, number of users in a queue needing slots are
> calculated based on whether users' jobs have any pending tasks.
> This works fine for map tasks. However, for reduce tasks, jobs do not need
> reduce slots until the minimum number of map tasks have been completed.
> Here, we add checking whether reduce is ready to schedule (i.e. if a job has
> completed enough map tasks) when we increment number of users in a queue
> needing reduce slots.
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