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From "Tom White (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4607) Race condition in ReduceTask completion can result in Task being incorrectly failed
Date Fri, 07 Sep 2012 20:42:08 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450954#comment-13450954

Tom White commented on MAPREDUCE-4607:

Please go ahead and make the changes and I'll review.
> Race condition in ReduceTask completion can result in Task being incorrectly failed
> -----------------------------------------------------------------------------------
>                 Key: MAPREDUCE-4607
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4607
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>    Affects Versions: 2.1.0-alpha
>            Reporter: Bikas Saha
>            Assignee: Bikas Saha
>         Attachments: MAPREDUCE-4607.1.patch, MAPREDUCE-4607.2.patch, MAPREDUCE-4607.3.patch,
> Problem reported by chackaravarthy in MAPREDUCE-4252
> This problem has been handled when speculative task launched for map task and other attempt
got failed (not killed)
> Can the similar kind of scenario can happen in case of reduce task?
> Consider the following scenario for reduce task in case of speculation (one attempt got
> 1. A task attempt is started.
> 2. A speculative task attempt for the same task is started.
> 3. The first task attempt completes and causes the task to transition to SUCCEEDED.
> 4. Then speculative task attempt will be killed because of the completion of first attempt.
> As a result, internal error will be thrown from this attempt (TaskImpl.MapRetroactiveKilledTransition)
and hence task attempt failure leads to job failure.
> TaskImpl.MapRetroactiveKilledTransition
> if (!TaskType.MAP.equals(task.getType())) {
>         LOG.error("Unexpected event for REDUCE task " + event.getType());
>         task.internalError(event.getType());
>       }
> So, do we need to have following code in MapRetroactiveKilledTransition also just like
in MapRetroactiveFailureTransition.
> if (event instanceof TaskTAttemptEvent) {
>         TaskTAttemptEvent castEvent = (TaskTAttemptEvent) event;
>         if (task.getState() == TaskState.SUCCEEDED &&
>             !castEvent.getTaskAttemptID().equals(task.successfulAttempt)) {
>           // don't allow a different task attempt to override a previous
>           // succeeded state
>           return TaskState.SUCCEEDED;
>         }
>       }
> please check whether this is a valid case and give your suggestion.

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