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https://issues.apache.org/jira/browse/HDFS-13183?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17111578#comment-17111578
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Jim Brennan commented on HDFS-13183:
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[~weichiu], [~hexiaoqiao], I believe this change is causing
TestBalancerWithNodeGroup to fail:
[https://ci-hadoop.apache.org/job/hadoop-qbt-trunk-java8-linux-x86_64/146/testReport/junit/org.apache.hadoop.hdfs.server.balancer/TestBalancerWithNodeGroup/testBalancerEndInNoMoveProgress/]
The problem is that Balancer.doBalance() was changed to construct the
NameNodeConnectors inside the iteration loop. The counter to track how many
iterations we have gone without a move ({{notChangedIterations}}) is in the
NameNodeConnector, but it is intended to work across iterations. Since we are
now creating new connectors on each iteration, this will always be zero, so we
will never exit a balancer with ExitStatus.NO_MOVE_PROGRESS.
> 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
>
>
> 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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