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https://issues.apache.org/jira/browse/HDFS-7597?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15183351#comment-15183351
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Chris Nauroth commented on HDFS-7597:
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bq. I'm still not sure why HDFS-8855 is/was necessary because this internal
patch solved the problem for us long ago.
Yes, agreed. That's why it was a forehead-smacking moment when I realized the
same issue essentially had been fixed twice mistakenly.
I agree that this patch is a more general solution. We might consider pulling
out HDFS-8855 later as a clean-up. As far as scope for this patch, do you want
to do something to address the {{TestDataNodeUGIProvider}} failure, and we'll
defer any further clean-up to a separate issue?
> DNs should not open new NN connections when webhdfs clients seek
> ----------------------------------------------------------------
>
> 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
> Labels: BB2015-05-TBR
> Attachments: HDFS-7597.patch, HDFS-7597.patch, 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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