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https://issues.apache.org/jira/browse/HADOOP-4116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12634927#action_12634927
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Hudson commented on HADOOP-4116:
--------------------------------

Integrated in Hadoop-trunk #615 (See 
[http://hudson.zones.apache.org/hudson/job/Hadoop-trunk/615/])

> Balancer should provide better resource management
> --------------------------------------------------
>
>                 Key: HADOOP-4116
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4116
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.17.0
>            Reporter: Raghu Angadi
>            Assignee: Hairong Kuang
>            Priority: Blocker
>             Fix For: 0.18.2, 0.19.0
>
>         Attachments: balancerRM.patch, balancerRM1.patch, 
> balancerRM2-b18.patch, balancerRM2.patch
>
>
> The number of threads are currently limited on datanodes. Once these threads 
> are occupied, DataNode does not accept any more requests (DOS). Recently we 
> saw a case where most of the 256 threads were waiting in 
> {{DataXceiver.replaceBlock()}} trying to acquire  {{balancingSem}}.  Since 
> rebalancing  is (heavily) throttled, I would think this would be the common 
> case. 
> These operations waiting  for active rebalancing threads to finish need not 
> take up a thread. 

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