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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1089) Fair Scheduler preemption triggers NPE when tasks are scheduled but not running
Date Mon, 19 Oct 2009 21:12:59 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1089?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12767547#action_12767547

Todd Lipcon commented on MAPREDUCE-1089:

Hi Matei,

I spent about 4 hours this morning attempting to get a unit test to demonstrate this behavior.
Unfortunately it's very difficult since the current test doesn't separate the scheduling of
a task and the beginning of the execution of that task. Despite my best efforts to get this
working, I haven't been able to. At this point I can't dedicate any more time to it - how
do you feel about committing as is without a test, or giving me some pointers on how to proceed
with testing?


> Fair Scheduler preemption triggers NPE when tasks are scheduled but not running
> -------------------------------------------------------------------------------
>                 Key: MAPREDUCE-1089
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1089
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: contrib/fair-share
>    Affects Versions: 0.21.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: mapreduce-1089.txt
> We see exceptions like this when preemption runs when a task has been scheduled on a
TT but has not yet started running.
> 2009-10-09 14:30:53,989 INFO org.apache.hadoop.mapred.FairScheduler: Should preempt 2
MAP tasks for job_200910091420_0006: tasksDueToMinShare = 2, tasksDueToFairShare = 0
> 2009-10-09 14:30:54,036 ERROR org.apache.hadoop.mapred.FairScheduler: Exception in fair
scheduler UpdateThread
> java.lang.NullPointerException
>         at org.apache.hadoop.mapred.FairScheduler$2.compare(FairScheduler.java:1015)
>         at org.apache.hadoop.mapred.FairScheduler$2.compare(FairScheduler.java:1013)
>         at java.util.Arrays.mergeSort(Arrays.java:1270)
>         at java.util.Arrays.sort(Arrays.java:1210)
>         at java.util.Collections.sort(Collections.java:159)
>         at org.apache.hadoop.mapred.FairScheduler.preemptTasks(FairScheduler.java:1013)
>         at org.apache.hadoop.mapred.FairScheduler.preemptTasksIfNecessary(FairScheduler.java:911)
>         at org.apache.hadoop.mapred.FairScheduler$UpdateThread.run(FairScheduler.java:286)

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