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From "Amar Kamat (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-4068) JobTracker might wrongly log a tip as failed
Date Thu, 04 Sep 2008 09:43:44 GMT
JobTracker might wrongly log a tip as failed

                 Key: HADOOP-4068
                 URL: https://issues.apache.org/jira/browse/HADOOP-4068
             Project: Hadoop Core
          Issue Type: Bug
          Components: mapred
            Reporter: Amar Kamat

Consider the following case
1) attempt _attempt_1_0_ from tip _tip_1_ that ran on tracker _tracker_1_ failed
2) jobtracker will mark _attempt_1_0_ for removal under _tracker_1_. Marking basically means
removal of the mapping _tracker_1_->_attempt_1_0_
3) Marked attempts are removed only on next heartbeat from _tracker__1 or when _tracker_1_
is lost.
4) Consider a case where _tracker_1_ goes down.
5) In the meanwhile attempt _attempt_1_1_ succeeds on _tracker_2_ and the jobtracker marks
the tip _tip_1_ as complete
6) Now the expiry-tracker thread detect that _tracker_1_ is lost and fails all the attempt
under _tracker_1_. 
7) Here the jobtracker will kill _attempt_1_0_ *again* and log tip _tip_1_ as failed in the
history although tip _tip_1_ is really complete/succeeded.

The events in the history file would be something like
tip_1 start
attempt_1_0 start
attempt_1_0 failed
attempt_1_1 start
attempt_1_1 finished
tip_1 finished
tip_1 failed

Note that this true even for tasks that expire. Tasks that are scheduled and never come back
are killed by the {{ExpireLaunchingTasks}} thread. It will also call {{JobInProgress.failedTask()}}
which will fail the attempt and log the TIP as failed.

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