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https://issues.apache.org/jira/browse/HADOOP-1374?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12562742#action_12562742
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Yunhong Gu commented on HADOOP-1374:
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I think I found the problem. It is caused by failed hostname resolving, so that
either JT or TT cannot get data from another node (because no network
connection can be set up), so it is blocked, for about 30 minutes.
> TaskTracker falls into an infinite loop.
> ----------------------------------------
>
> Key: HADOOP-1374
> URL: https://issues.apache.org/jira/browse/HADOOP-1374
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.12.3
> Reporter: Konstantin Shvachko
> Assignee: Arun C Murthy
> Attachments: DataNode1.log, DataNode2.log,
> hadoop-1374-yunhong.tar.gz, JobTracker.log, NameNode.log, TaskTracker1.log,
> TaskTracker2.log, TestDFSIO.log
>
>
> All maps had been completed successfully. I had only one reduce task during
> which
> TaskTracker infinitely outputs:
> 07/05/15 19:35:41 INFO mapred.TaskTracker: task_0001_r_000000_0 0.16666667%
> reduce > copy (4 of 8 at 0.00 MB/s) >
> 07/05/15 19:35:42 INFO mapred.TaskTracker: task_0001_r_000000_0 0.16666667%
> reduce > copy (4 of 8 at 0.00 MB/s) >
> 07/05/15 19:35:43 INFO mapred.TaskTracker: task_0001_r_000000_0 0.16666667%
> reduce > copy (4 of 8 at 0.00 MB/s) >
> 07/05/15 19:35:44 INFO mapred.TaskTracker: task_0001_r_000000_0 0.16666667%
> reduce > copy (4 of 8 at 0.00 MB/s) >
> 07/05/15 19:35:45 INFO mapred.TaskTracker: task_0001_r_000000_0 0.16666667%
> reduce > copy (4 of 8 at 0.00 MB/s) >
> JobTracker does not log anything about task task_0001_r_000000_0 except for
> 07/05/15 19:49:01 INFO mapred.JobTracker: Adding task 'task_0001_r_000000_0'
> to tip tip_0001_r_000000, for tracker 'tracker_my-host.com:50050'
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