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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7915) The DataNode can sometimes allocate a ShortCircuitShm slot and fail to tell the DFSClient about it because of a network error
Date Fri, 13 Mar 2015 22:36:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14361218#comment-14361218
] 

Chris Nauroth commented on HDFS-7915:
-------------------------------------

I'm repeating my earlier comment in case it got lost while focusing on the admittedly much
more important discussion about the actual bug.

{quote}
Thanks for the patch, Colin. The change looks good. In the test, is the Visitor indirection
necessary, or would it be easier to add 2 VisibleForTesting getters that return the segments
and slots directly to the test code?
{quote}


> The DataNode can sometimes allocate a ShortCircuitShm slot and fail to tell the DFSClient
about it because of a network error
> -----------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-7915
>                 URL: https://issues.apache.org/jira/browse/HDFS-7915
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.7.0
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>         Attachments: HDFS-7915.001.patch, HDFS-7915.002.patch, HDFS-7915.004.patch, HDFS-7915.005.patch
>
>
> The DataNode can sometimes allocate a ShortCircuitShm slot and fail to tell the DFSClient
about it because of a network error.  In {{DataXceiver#requestShortCircuitFds}}, the DataNode
can succeed at the first part (mark the slot as used) and fail at the second part (tell the
DFSClient what it did). The "try" block for unregistering the slot only covers a failure in
the first part, not the second part. In this way, a divergence can form between the views
of which slots are allocated on DFSClient and on server.



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