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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7597) Clients seeking over webhdfs may crash the NN
Date Thu, 15 Jan 2015 18:12:37 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7597?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14279042#comment-14279042
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Daryn Sharp commented on HDFS-7597:
-----------------------------------

I meant to say the map that the builder actually creates.  The code for get/put is substantially
more complicated than {{LRUMap}} so it can provide features we don't need in this use case.

Maybe a CHM would be faster.  I went with a simple solution to resolve recurring production
issues.  I'll try to run some quick benchmarks.

The test failure is due to the way the test is written.  I need to update it.



> 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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