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https://issues.apache.org/jira/browse/MAPREDUCE-754?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12731264#action_12731264
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Amareshwari Sriramadasu commented on MAPREDUCE-754:
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Blacklisting should not add and remove hosts to the uniqueHostsMap. It should
just do a get to get the number and the update should happen only in
updateTaskTrackerStatus method.
> NPE in expiry thread when a TT is lost
> --------------------------------------
>
> Key: MAPREDUCE-754
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-754
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: jobtracker
> Reporter: Ramya R
> Priority: Minor
> Attachments: mapreduce-754-wip.patch
>
>
> NullPointerException is obtained in Tracker Expiry Thread. Below is the
> exception obtained in the JT logs
> {noformat}
> ERROR org.apache.hadoop.mapred.JobTracker: Tracker Expiry Thread got
> exception: java.lang.NullPointerException
> at
> org.apache.hadoop.mapred.JobTracker.updateTaskTrackerStatus(JobTracker.java:2971)
> at org.apache.hadoop.mapred.JobTracker.access$300(JobTracker.java:104)
> at
> org.apache.hadoop.mapred.JobTracker$ExpireTrackers.run(JobTracker.java:381)
> at java.lang.Thread.run(Thread.java:619)
> {noformat}
> The steps to reproduce this issue are:
> * Blacklist a TT.
> * Restart it.
> * The above exception is obtained when the first instance of TT is marked as
> lost.
> However the above exception does not break any functionality.
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