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https://issues.apache.org/jira/browse/HDFS-13183?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16377367#comment-16377367
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Ajay Kumar commented on HDFS-13183:
-----------------------------------
[~hexiaoqiao], there are broader efforts to utilize SNN in this kind of
scenario. (check [HDFS-12975]) Individual change to one function will be
difficult to track and may break important functionality.
> 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: Improvement
> Components: balancer & mover, namenode
> Affects Versions: 2.7.5, 3.1.0, 2.9.1, 2.8.4, 3.0.2
> Reporter: He Xiaoqiao
> Assignee: He Xiaoqiao
> Priority: Major
> Attachments: HDFS-13183-trunk.001.patch, HDFS-13183-trunk.002.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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