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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3590) Null pointer exception in JobTracker when the task tracker is not yet resolved
Date Wed, 18 Jun 2008 06:00:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12605855#action_12605855

Devaraj Das commented on HADOOP-3590:

I'd go with an option where the tasktracker returns empty-handed. This will keep things simple
at the cost of wasting very few cycles while the JobTracker is resolving the tasktracker.

> Null pointer exception in JobTracker when the task tracker is not yet resolved
> ------------------------------------------------------------------------------
>                 Key: HADOOP-3590
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3590
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Amar Kamat
>            Assignee: Amar Kamat
>            Priority: Blocker
>             Fix For: 0.18.0
> 2008-06-17 13:29:56,711 INFO org.apache.hadoop.mapred.JobTracker: Got heartbeat from:
xxx (initialContact: false acceptNewTasks: true) with responseId: 0
> 2008-06-17 13:29:56,711 INFO org.apache.hadoop.ipc.Server: IPC Server handler 7 on 123,
call heartbeat(org.apache.hadoop.mapred.TaskTrackerStatus@123, true, true, -1) from xxx error:
java.io.IOException: java.lang.NullPointerException
> java.io.IOException: java.lang.NullPointerException
>        at org.apache.hadoop.mapred.JobTracker.getParentNode(JobTracker.java:1327)
>        at org.apache.hadoop.mapred.JobInProgress.findNewMapTask(JobInProgress.java:1142)
>        at org.apache.hadoop.mapred.JobInProgress.obtainNewMapTask(JobInProgress.java:685)
>        at org.apache.hadoop.mapred.JobTracker.getNewTaskForTaskTracker(JobTracker.java:1708)
>        at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:1431)
>        at sun.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
>        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>        at java.lang.reflect.Method.invoke(Method.java:597)
>        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:452)
>        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:888)
> ----
> Looks like a corner case. This happens when the task tracker just joins the JT and asks
for a task to run. In a case where the task tracker is not yet resolved, this can lead to
null pointer exception. Remember that the task trackers are  added to separate queue and resolved
by a separate thread i.e there is no forced resolution for task trackers. There is no side
effect of this bug since the task tracker will try again and also the job runs to completion.

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