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https://issues.apache.org/jira/browse/HDFS-14882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16941143#comment-16941143
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Lukas Majercak commented on HDFS-14882:
---------------------------------------

Overall looks okay to me, seems like an improvement of 
dfs.namenode.avoid.read.highload.datanode (+ .threshold). I only wish we could 
also use some sort of an estimate of load that we've already scheduled on each 
DN, not just xceivers reported by them. 

> Consider DataNode load when #getBlockLocation
> ---------------------------------------------
>
>                 Key: HDFS-14882
>                 URL: https://issues.apache.org/jira/browse/HDFS-14882
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>            Reporter: Xiaoqiao He
>            Assignee: Xiaoqiao He
>            Priority: Major
>         Attachments: HDFS-14882.001.patch
>
>
> Currently, we consider load of datanode when #chooseTarget for writer, 
> however not consider it for reader. Thus, the process slot of datanode could 
> be occupied by #BlockSender for reader, and disk/network will be busy 
> workload, then meet some slow node exception. IIRC same case is reported 
> times. Based on the fact, I propose to consider load for reader same as it 
> did #chooseTarget for writer.



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