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https://issues.apache.org/jira/browse/MAPREDUCE-754?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12777389#action_12777389
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Hemanth Yamijala commented on MAPREDUCE-754:
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This patch introduces a bug in getNumberOfUniqueHosts. It subtracts the number
of blacklisted trackers from the number of unique hosts, which is incorrect if
multiple trackers are running on a host.
> 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
> Affects Versions: 0.20.1
> Reporter: Ramya R
> Assignee: Amar Kamat
> Priority: Minor
> Fix For: 0.22.0
>
> Attachments: mapreduce-754-v1.1.patch, mapreduce-754-v1.2.patch,
> 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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