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https://issues.apache.org/jira/browse/HADOOP-4116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12633816#action_12633816
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Raghu Angadi commented on HADOOP-4116:
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> 3. The balancer does not set a timeout on a socket. Instead, it sets the
> option KeepAlive on the socket. So a block move does not timeout no matter
> how slow it goes and next phrase of scheduling does not get started when
> there is a pending block move.
How does keep-alive matter? TCP has no inherent timeout for a connection in
normal state.
> 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
>
>
> 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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