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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 Wed, 05 Sep 2012 10:20:07 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13448613#comment-13448613
] 

Tom White commented on MAPREDUCE-4607:
--------------------------------------

Generally looks good.

* In TestTaskImpl the new methods don't actually test the reduce task type since the setup
method is run before taskType is mutated to TaskType.REDUCE. You can fix this by changing
the taskType instance to be a parameter that is passed when creating the mockTask, and in
the reduce tests create a new mockTask that has the correct task type.
* Use Preconditions.checkArgument rather than Java asserts, since the latter are not normally
enabled.
* In TaskImpl remove comment "only possible for map tasks"
* "import org.mortbay.log.Log" looks spurious.
                
> 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
>
>
> 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
killed):
> 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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