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Date: Mon, 15 Oct 2012 20:47:05 +0000 (UTC)
From: "Eli Collins (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-3990) NN's health report has severe
 performance problems
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    [ https://issues.apache.org/jira/browse/HDFS-3990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13476429#comment-13476429 ] 

Eli Collins commented on HDFS-3990:
-----------------------------------

Why not use the DatanodeID hostName field instead of calling and caching InetAddress#getByName in the NN? The DN has already done the lookup (modulo the tests which use dfs.datanode.hostname) and this way we don't have to worry about inconsistency between the nodeAddr and the ipAddr/hostName fields. For sanity the NN could do a lookup when the DN registers and compare it's value to the DN reported one.

Comments on this patch:
- In registerDatanode why is OK to no longer update the registration info with the reported IP?
- The comments in DatanodeManager ("Mostly called inside an RPC.".. and "Update the IP to the address of the RPC request"..) are no longer accurate after your change.
                
> 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: name-node
>    Affects Versions: 0.23.0, 2.0.0-alpha, 3.0.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>         Attachments: HDFS-3990.patch, HDFS-3990.patch
>
>
> 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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