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https://issues.apache.org/jira/browse/HDFS-3990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13791096#comment-13791096
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Tsz Wo (Nicholas), SZE commented on HDFS-3990:
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The hostname.equals(ip) check added to DatanodeManager.registerDatanode(..) may
not work for existing clusters which do not have reverse DNS lookup support;
filed HDFS-5338.
> 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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