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https://issues.apache.org/jira/browse/HDFS-6840?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14106428#comment-14106428
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Ashwin Shankar commented on HDFS-6840:
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Since we are planning to make a 2.5.1 release, should this jira be made a 
blocker for 2.5.1 ?


> Clients are always sent to the same datanode when read is off rack
> ------------------------------------------------------------------
>
>                 Key: HDFS-6840
>                 URL: https://issues.apache.org/jira/browse/HDFS-6840
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.5.0
>            Reporter: Jason Lowe
>            Assignee: Andrew Wang
>            Priority: Critical
>
> After HDFS-6268 the sorting order of block locations is deterministic for a 
> given block and locality level (e.g.: local, rack. off-rack), so off-rack 
> clients all see the same datanode for the same block.  This leads to very 
> poor behavior in distributed cache localization and other scenarios where 
> many clients all want the same block data at approximately the same time.  
> The one datanode is crushed by the load while the other replicas only handle 
> local and rack-local requests.



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