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https://issues.apache.org/jira/browse/HDFS-13183?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17112463#comment-17112463
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Xiaoqiao He commented on HDFS-13183:
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Thanks [~Jim_Brennan] for your information. I think TestBalancer should not be
affected even with this feature, because configuration
`dfs.ha.allow.stale.reads` not set true in TestBalancer and all logic will keep
the same. Actually I try to instead `Balancer.run(namenodes,
BalancerParameters.DEFAULT, conf);` with `Balancer.run(namenodes, nsIds,
BalancerParameters.DEFAULT, conf);` offline, and all case of TestBalancer could
pass at local.
The new addendum patch just improve log output.
About failed unit test
{{TestBalancerWithHANameNodes.testBalancerWithObserver}}, I try to run many
times at local without the changes, it is also low-probability failure, And I
try to trace the code execution path, it looks no difference between patch and
no patch. [~xkrogen] Would you mind to have another check?
> 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,
> 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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