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https://issues.apache.org/jira/browse/HADOOP-5214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12672509#action_12672509
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Vinod K V commented on HADOOP-5214:
-----------------------------------
Here's the trace.
{code}
2009-02-08 16:27:57,496 ERROR org.apache.hadoop.mapred.FairScheduler: Failed to
update fair share calculations
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
at java.util.HashMap$ValueIterator.next(HashMap.java:822)
at
org.apache.hadoop.mapred.FairScheduler.getTotalSlots(FairScheduler.java:703)
at
org.apache.hadoop.mapred.FairScheduler.updateFairShares(FairScheduler.java:622)
at org.apache.hadoop.mapred.FairScheduler.update(FairScheduler.java:358)
at
org.apache.hadoop.mapred.FairScheduler$UpdateThread.run(FairScheduler.java:212)
2009-02-08 16:27:57,500 ERROR org.apache.hadoop.mapred.JobTracker: Tracker
Expiry Thread got exception: java.lang.NullPointerException
{code}
And the underlying problem is that getTotalSlots gets the list of trackers via
TaskTrackerManager.taskTrackers() and iterates through it to calculate the
total number of map and reduce slots in the cluster. The exception occurs when
JT internally modifies the list of TaskTrackers for e.g while updating the list
of lost TaskTrackers.
This information is already available via ClusterStatus. Using it will fix the
issue.
> ConcurrentModificationException in FairScheduler.getTotalSlots
> --------------------------------------------------------------
>
> Key: HADOOP-5214
> URL: https://issues.apache.org/jira/browse/HADOOP-5214
> Project: Hadoop Core
> Issue Type: Bug
> Components: contrib/fair-share
> Reporter: Vinod K V
>
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