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https://issues.apache.org/jira/browse/YARN-8436?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16548144#comment-16548144
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genericqa commented on YARN-8436:
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| JIRA Issue | YARN-8436 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12932098/YARN-8436.003.patch |
| Console output | 
https://builds.apache.org/job/PreCommit-YARN-Build/21283/console |
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This message was automatically generated.



> FSParentQueue: Comparison method violates its general contract
> --------------------------------------------------------------
>
>                 Key: YARN-8436
>                 URL: https://issues.apache.org/jira/browse/YARN-8436
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: fairscheduler
>    Affects Versions: 3.1.0
>            Reporter: Wilfred Spiegelenburg
>            Assignee: Wilfred Spiegelenburg
>            Priority: Minor
>         Attachments: YARN-8436.001.patch, YARN-8436.002.patch, 
> YARN-8436.003.patch
>
>
> The ResourceManager can fail while sorting queues if an update comes in:
> {code:java}
> FATAL org.apache.hadoop.yarn.server.resourcemanager.ResourceManager: Error in 
> handling event type NODE_UPDATE to the scheduler
> java.lang.IllegalArgumentException: Comparison method violates its general 
> contract!
>       at java.util.TimSort.mergeLo(TimSort.java:777)
>       at java.util.TimSort.mergeAt(TimSort.java:514)
> ...
>       at java.util.Collections.sort(Collections.java:175)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FSParentQueue.assignContainer(FSParentQueue.java:223){code}
> The reason it breaks is a change in the sorted object itself. 
> This is why it fails:
>  * an update from a node comes in as a heartbeat.
>  * the update triggers a check to see if we can assign a container on the 
> node.
>  * walk over the queue hierarchy to find a queue to assign a container to: 
> top down.
>  * for each parent queue we sort the child queues in {{assignContainer}} to 
> decide which queue to descent into.
>  * we lock the parent queue when sort to prevent changes, but we do not lock 
> the child queues that we are sorting.
> If during this sorting a different node update changes a child queue then we 
> allow that. This means that the objects that we are trying to sort now might 
> be out of order. That causes the issue with the comparator. The comparator 
> itself is not broken.



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