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https://issues.apache.org/jira/browse/HDFS-10702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15608805#comment-15608805
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Sean Mackrory commented on HDFS-10702:
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I think we should also consider ways to not send requests to multiple SNNs. I 
did some testing, and while this does indeed decrease traffic to the NN and 
increase performance when a single SNN is there, if you have multiple SNNs this 
only decreases traffic to the NN - it actually also decreases the performance 
of the client and would further increase overall network usage. I don't think 
we need to be particularly sophisticated about picking the most ideal SNN, 
especially since this feature inherently accepts the idea of not having the 
most up to date metadata.

> Add a Client API and Proxy Provider to enable stale read from Standby
> ---------------------------------------------------------------------
>
>                 Key: HDFS-10702
>                 URL: https://issues.apache.org/jira/browse/HDFS-10702
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Jiayi Zhou
>            Assignee: Jiayi Zhou
>            Priority: Minor
>         Attachments: HDFS-10702.001.patch, HDFS-10702.002.patch, 
> HDFS-10702.003.patch, HDFS-10702.004.patch, HDFS-10702.005.patch, 
> StaleReadfromStandbyNN.pdf
>
>
> Currently, clients must always talk to the active NameNode when performing 
> any metadata operation, which means active NameNode could be a bottleneck for 
> scalability. One way to solve this problem is to send read-only operations to 
> Standby NameNode. The disadvantage is that it might be a stale read. 
> Here, I'm thinking of adding a Client API to enable/disable stale read from 
> Standby which gives Client the power to set the staleness restriction.



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