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https://issues.apache.org/jira/browse/HADOOP-15317?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16401149#comment-16401149
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Ajay Kumar edited comment on HADOOP-15317 at 3/15/18 9:52 PM:
--------------------------------------------------------------
[~xiaochen], thanks for working on this.
Two comments:
* Current change in do.while loop introduces a bug when {{if (excludedNodes ==
null || !excludedNodes.contains(ret))}} is not true even once. In this case we
will return the last allocated value of {{ret = innerNode.getLeaf(leaveIndex,
node);}}.
To mitigate this we can reinitialize ret with null in else clause.
{code:java}
if (excludedNodes == null || !excludedNodes.contains(ret)) {
break;
} else {
ret = null;
LOG.debug("Node {} is excluded, continuing.", ret);
}{code}
* Shall we add {{numOfDatanodes}} in debug statement at L525.
was (Author: ajayydv):
[~xiaochen], thanks for working on this.
Two comments:
* Current change in do.while loop introduces a bug in case when {{if
(excludedNodes == null || !excludedNodes.contains(ret))}} is not true even
once. In this case we will return the last allocated value of {{ret =
innerNode.getLeaf(leaveIndex, node);}}.
To mitigate this we can reinitialize ret with null in else clause.
{code}if (excludedNodes == null || !excludedNodes.contains(ret)) {
break;
} else {
ret = null;
LOG.debug("Node {} is excluded, continuing.", ret);
}{code}
* Shall we add {{numOfDatanodes}} in debug statement at L525.
> 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
>
>
> 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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