Wilfred Spiegelenburg created YARN-8436:
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Summary: 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
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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