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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7597) Clients seeking over webhdfs may crash the NN
Date Fri, 09 Jan 2015 21:35:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7597?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14271904#comment-14271904
] 

Chris Nauroth commented on HDFS-7597:
-------------------------------------

Hi [~daryn].  Thanks for the patch.  This looks good.  Regarding the brief race condition,
would it make sense to make the whole get-and-conditional-put operation synchronized on {{ugiCache}}?

> Clients seeking over webhdfs may crash the NN
> ---------------------------------------------
>
>                 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
>         Attachments: 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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