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https://issues.apache.org/jira/browse/MAPREDUCE-5744?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Karthik Kambatla updated MAPREDUCE-5744:
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Status: Patch Available (was: Reopened)
> Job hangs because RMContainerAllocator$AssignedRequests.preemptReduce()
> violates the comparator contract
> --------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-5744
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5744
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 2.0.5-alpha
> Reporter: Sangjin Lee
> Assignee: Gera Shegalov
> Priority: Blocker
> Attachments: MAPREDUCE-5744.v02.patch
>
>
> We ran into a situation where tasks are not getting assigned because
> RMContainerAllocator$AssignedRequests.preemptReduce() fails repeatedly with
> the following exception:
> {code}
> 2014-02-06 16:43:45,183 ERROR [RMCommunicator Allocator]
> org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: ERROR IN
> CONTACTING RM.
> java.lang.IllegalArgumentException: Comparison method violates its general
> contract!
> at java.util.TimSort.mergeLo(TimSort.java:747)
> at java.util.TimSort.mergeAt(TimSort.java:483)
> at java.util.TimSort.mergeCollapse(TimSort.java:408)
> at java.util.TimSort.sort(TimSort.java:214)
> at java.util.TimSort.sort(TimSort.java:173)
> at java.util.Arrays.sort(Arrays.java:659)
> at java.util.Collections.sort(Collections.java:217)
> at
> org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator$AssignedRequests.preemptReduce(RMContainerAllocator.java:1106)
> at
> org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator.preemptReducesIfNeeded(RMContainerAllocator.java:416)
> at
> org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator.heartbeat(RMContainerAllocator.java:230)
> at
> org.apache.hadoop.mapreduce.v2.app.rm.RMCommunicator$1.run(RMCommunicator.java:252)
> at java.lang.Thread.run(Thread.java:744)
> {code}
> It is because the comparator that's defined in this method does not abide by
> the contract, specifically if p == 0.
> Comparator.compare():
> http://docs.oracle.com/javase/7/docs/api/java/util/Comparator.html#compare(T,
> T)
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