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https://issues.apache.org/jira/browse/HDFS-3990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13508879#comment-13508879
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Daryn Sharp commented on HDFS-3990:
-----------------------------------

The check was floated up out of {{DatanodeManager.checkInList}} which rejected 
unresolvable nodes.  Is it that {{InetAddress.getByName}} on windows doesn't 
resolve 127.0.0.1 and doesn't throw {{UnknownHostException}}, which makes it 
appear it didn't resolve?  I seem to have vague recollection of a similar issue 
before.


                
> NN's health report has severe performance problems
> --------------------------------------------------
>
>                 Key: HDFS-3990
>                 URL: https://issues.apache.org/jira/browse/HDFS-3990
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 0.23.0, 2.0.0-alpha, 3.0.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>             Fix For: 3.0.0, 2.0.3-alpha, 0.23.5
>
>         Attachments: HDFS-3990.branch-0.23.patch, 
> HDFS-3990.branch-0.23.patch, HDFS-3990.patch, HDFS-3990.patch, 
> HDFS-3990.patch, HDFS-3990.patch, HDFS-3990.patch, HDFS-3990.patch, 
> HDFS-3990.patch, HDFS-3990.patch, hdfs-3990.txt, hdfs-3990.txt
>
>
> The dfshealth page will place a read lock on the namespace while it does a 
> dns lookup for every DN.  On a multi-thousand node cluster, this often 
> results in 10s+ load time for the health page.  10 concurrent requests were 
> found to cause 7m+ load times during which time write operations blocked.

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