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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1289) Just launched tasks aren't getting cleaned up on job completion (success/killed)
Date Mon, 23 Apr 2007 17:50:15 GMT
Just launched tasks aren't getting cleaned up on job completion (success/killed)

                 Key: HADOOP-1289
                 URL: https://issues.apache.org/jira/browse/HADOOP-1289
             Project: Hadoop
          Issue Type: Bug
          Components: mapred
            Reporter: Arun C Murthy

When a job is killed, if there are tasks which haven't been launched yet (just scheduled on
a tasktracker) it leads to a situation where the non-launched task hangs around for a long
time on the tasktrackers taking up valuable 'slots' preventing the scheduling of _legitimate_
tasks on them.

This is due to a race-condition:
a) Job is killed:
    -> JobInProgress.garbageCollect
    -> JobInProgress.finalizeJob
    -> JobTracker.removeJobTasks
    -> JobTracker.removeTaskEntry - this removes the taskid -> TIP entry in JobTracker.taskIdToTIPMap
b) ExpireLaunchingTasks thread detects the task has timedout, however since the taskid ->
TIP map is missing it cannot 'fail' the task - thus leaving it orphaned on the tasktracker.

One possible solution is to broadcast a KillJobAction to all trackers in the cluster (or only
those trackers which ever ran a task of this Job) ensuring the right cleanup... clearly this
is a hairy situation.


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