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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7597) DNs should not open new NN connections when webhdfs clients seek
Date Mon, 07 Mar 2016 14:58:41 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7597?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15183095#comment-15183095
] 

Daryn Sharp commented on HDFS-7597:
-----------------------------------

[~cnauroth] We can re-brand this as a more general improvement since it helps not only the
DN but also the NN by reducing the per-connection UGI instances.  I'm still not sure why HDFS-8855
is/was necessary because this internal patch solved the problem for us long ago.

> 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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