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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 19:17:36 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7597?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14279143#comment-14279143
] 

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

Did some quick and dirty tests.  I tried to put the sync'ed {{LRUMap}} at a disadvantage by
being reader heavy.  A concurrent & bounded {{CacheBuilder}} map performs a bit slower
but has wild variance whereas {{LRUMap}} is pretty stable.   CB also increased the heap ~4-10X
over the {{LRUMap}}.

> 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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