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Date: Mon, 23 May 2016 21:43:12 +0000 (UTC)
From: "Xiao Chen (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12766514.1420832858000.270309.1464039792907@Atlassian.JIRA>
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Subject: [jira] [Commented] (HDFS-7597) DNs should not open new NN
 connections when webhdfs clients seek
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archived-at: Mon, 23 May 2016 21:43:14 -0000


    [ https://issues.apache.org/jira/browse/HDFS-7597?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15297148#comment-15297148 ] 

Xiao Chen commented on HDFS-7597:
---------------------------------

Thanks all for the contribution and discussion.

[~cnauroth], do you think we can move forward to commit this patch? Please let me know if there's anything I can help with. Thanks!

> DNs should not open new NN connections when webhdfs clients seek
> ----------------------------------------------------------------
>
>                 Key: HDFS-7597
>                 URL: https://issues.apache.org/jira/browse/HDFS-7597
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: webhdfs
>    Affects Versions: 2.0.0-alpha
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>              Labels: BB2015-05-TBR
>         Attachments: HDFS-7597.patch, HDFS-7597.patch, HDFS-7597.patch
>
>
> Webhdfs seeks involve closing the current connection, and reissuing a new open request with the new offset.  The RPC layer caches connections so the DN keeps a lingering connection open to the NN.  Connection caching is in part based on UGI.  Although the client used the same token for the new offset request, the UGI is different which forces the DN to open another unnecessary connection to the NN.
> A job that performs many seeks will easily crash the NN due to fd exhaustion.


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