[jira] Commented: (HADOOP-4116) Balancer should provide better resource management

["Raghu Angadi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-4116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12630652#action_12630652 ] 

Raghu Angadi commented on HADOOP-4116:
--------------------------------------

Thanks for the detailed analysis Hairong. I filed the original jira just looking at one symptom.

> Balancer should provide better resource management
> --------------------------------------------------
>
>                 Key: HADOOP-4116
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4116
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.17.0
>            Reporter: Raghu Angadi
>            Assignee: Hairong Kuang
>
> 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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