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https://issues.apache.org/jira/browse/YARN-8436?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16620509#comment-16620509
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stefanlee commented on YARN-8436:
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[~wilfreds] thanks for this jira, As you mentioned above:
{quote}If during this sorting a different node update changes a child queue
then we allow that.
{quote}
doesn't RM handle NODE_UPDATE event one by one?
> 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
> Fix For: 3.2.0
>
> 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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