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From "Xiao Chen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-15317) Improve NetworkTopology chooseRandom's loop
Date Thu, 29 Mar 2018 21:39:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15317?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16419805#comment-16419805
] 

Xiao Chen commented on HADOOP-15317:
------------------------------------

That was intentional, as that's the number of nodes under the specified scope aka. {{innerNode.getNumOfLeaves()}}.

InĀ [^HADOOP-15317.06.patch]I renamed it to {{totalInScopeNodes}} to make it more intuitive.
The word 'available' is confusing, because it would need a definition and will collide with
the last param, {{availableNodes}}. Javadoc also has the explanation, LMK if you have an idea
on how to improve that.

> 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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