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https://issues.apache.org/jira/browse/HADOOP-15317?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16416876#comment-16416876
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Xiao Chen commented on HADOOP-15317:
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Thanks for the review Eddy.
[^HADOOP-15317.05.patch] addressed the comments. As synced offline, the reason
for {{lastValidNode}} is only because we're not sure what exactly caused the
initial bug (infinite loop). Theoretically it should not happen, but this will
give us some insights if it does happen.... Changed the log to error to make it
easier to be found.
> 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
>
>
> 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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