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https://issues.apache.org/jira/browse/HADOOP-15317?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16423267#comment-16423267
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Lei (Eddy) Xu commented on HADOOP-15317:
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+1. Thanks [~xiaochen]!
> Improve NetworkTopology chooseRandom's loop
> -------------------------------------------
>
> Key: HADOOP-15317
> URL: https://issues.apache.org/jira/browse/HADOOP-15317
> Project: Hadoop Common
> Issue Type: Bug
> Reporter: Xiao Chen
> Assignee: Xiao Chen
> Priority: Major
> Attachments: HADOOP-15317.01.patch, HADOOP-15317.02.patch,
> HADOOP-15317.03.patch, HADOOP-15317.04.patch, HADOOP-15317.05.patch,
> HADOOP-15317.06.patch, Screen Shot 2018-03-28 at 7.23.32 PM.png
>
>
> Recently we found a postmortem case where the ANN seems to be in an infinite
> loop. From the logs it seems it just went through a rolling restart, and DNs
> are getting registered.
> Later the NN become unresponsive, and from the stacktrace it's inside a
> do-while loop inside {{NetworkTopology#chooseRandom}} - part of what's done
> in HDFS-10320.
> Going through the code and logs I'm not able to come up with any theory
> (thought about incorrect locking, or the Node object being modified outside
> of NetworkTopology, both seem impossible) why this is happening, but we
> should eliminate this loop.
> stacktrace:
> {noformat}
> Stack:
> java.util.HashMap.hash(HashMap.java:338)
> java.util.HashMap.containsKey(HashMap.java:595)
> java.util.HashSet.contains(HashSet.java:203)
> org.apache.hadoop.net.NetworkTopology.chooseRandom(NetworkTopology.java:786)
> org.apache.hadoop.net.NetworkTopology.chooseRandom(NetworkTopology.java:732)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseDataNode(BlockPlacementPolicyDefault.java:757)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseRandom(BlockPlacementPolicyDefault.java:692)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseRandom(BlockPlacementPolicyDefault.java:666)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseLocalRack(BlockPlacementPolicyDefault.java:573)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTargetInOrder(BlockPlacementPolicyDefault.java:461)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:368)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:243)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:115)
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget4AdditionalDatanode(BlockManager.java:1596)
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalDatanode(FSNamesystem.java:3599)
> org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.getAdditionalDatanode(NameNodeRpcServer.java:717)
> {noformat}
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