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