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https://issues.apache.org/jira/browse/HDFS-13183?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiaoqiao He updated HDFS-13183:
-------------------------------
    Attachment: HDFS-13183.addendum.patch
        Status: Patch Available  (was: Reopened)

[~weichiu],[~Jim_Brennan] upload addendum patch and try to trigger yetus again. 
PTAL.
addendum try to select standby namenode when invoke #getBlocks rather than 
create NameNodeConnector instance for each iterator. Unit tests 
{{TestBalancerWithNodeGroup}} passed at local. Let's see what yetus say.

> Standby NameNode process getBlocks request to reduce Active load
> ----------------------------------------------------------------
>
>                 Key: HDFS-13183
>                 URL: https://issues.apache.org/jira/browse/HDFS-13183
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: balancer & mover, namenode
>            Reporter: Xiaoqiao He
>            Assignee: Xiaoqiao He
>            Priority: Major
>             Fix For: 3.3.1, 3.4.0
>
>         Attachments: HDFS-13183-trunk.001.patch, HDFS-13183-trunk.002.patch, 
> HDFS-13183-trunk.003.patch, HDFS-13183.004.patch, HDFS-13183.005.patch, 
> HDFS-13183.006.patch, HDFS-13183.007.patch, HDFS-13183.addendum.patch
>
>
> The performance of Active NameNode could be impact when {{Balancer}} requests 
> #getBlocks, since query blocks of overly full DNs performance is extremely 
> inefficient currently. The main reason is {{NameNodeRpcServer#getBlocks}} 
> hold read lock for long time. In extreme case, all handlers of Active 
> NameNode RPC server are occupied by one reader 
> {{NameNodeRpcServer#getBlocks}} and other write operation calls, thus Active 
> NameNode enter a state of false death for number of seconds even for minutes.
> The similar performance concerns of Balancer have reported by HDFS-9412, 
> HDFS-7967, etc.
> If Standby NameNode can shoulder #getBlocks heavy burden, it could speed up 
> the progress of balancing and reduce performance impact to Active NameNode.



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