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https://issues.apache.org/jira/browse/HDFS-9198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14968345#comment-14968345
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Uma Maheswara Rao G commented on HDFS-9198:
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Ok, I have just looked your first comments which is trying to answer #5

> Coalesce IBR processing in the NN
> ---------------------------------
>
>                 Key: HDFS-9198
>                 URL: https://issues.apache.org/jira/browse/HDFS-9198
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.0.0-alpha
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>         Attachments: HDFS-9198-branch2.patch, HDFS-9198-trunk.patch, 
> HDFS-9198-trunk.patch, HDFS-9198-trunk.patch
>
>
> IBRs from thousands of DNs under load will degrade NN performance due to 
> excessive write-lock contention from multiple IPC handler threads.  The IBR 
> processing is quick, so the lock contention may be reduced by coalescing 
> multiple IBRs into a single write-lock transaction.  The handlers will also 
> be freed up faster for other operations.



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