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https://issues.apache.org/jira/browse/HADOOP-4116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12634074#action_12634074
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Steve Loughran commented on HADOOP-4116:
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keepAlives are a fairly weak way of assessing "liveness" because
-it works at the network stack level, so your app may still be dead but the KA
packets are happy
-if there are a lot of (idle) connections between two hosts, a lot of KA
traffic can be generated, rather than one packet per host, which is how a lot
of protocols (CORBA and DCOM, for example) communicate "we are still alive".
I think this proposal is better than nothing, but we need to be aware of
limitations. It will detect a network partition, but not a hung far end if the
network stack is still up
> 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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