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https://issues.apache.org/jira/browse/HDFS-14523?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16904270#comment-16904270
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Wei-Chiu Chuang commented on HDFS-14523:
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Patch still applies. [~vagarychen] any chance you can take a look?

> Remove excess read lock for NetworkToplogy
> ------------------------------------------
>
>                 Key: HDFS-14523
>                 URL: https://issues.apache.org/jira/browse/HDFS-14523
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Wu Weiwei
>            Assignee: Wu Weiwei
>            Priority: Major
>         Attachments: HDFS-14523.1.patch
>
>
> getNumOfRacks() and getNumOfLeaves() are two high frequencies call methods 
> for BlockPlacementPolicy, this two methods need to get NetworkTopology read 
> lock, and get lock in high frequencies call methods may impact the namenode 
> performance. 
> This two methods get number of racks and number of leaves just for 
> chooseTarget calculate,  lock in these two methods cannot guarantee these two 
> values will not change in the subsequent calculations.
> I think it's safe to remove the read lock from this two methods.



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