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https://issues.apache.org/jira/browse/MAPREDUCE-4607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13449806#comment-13449806
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Bikas Saha commented on MAPREDUCE-4607:
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I see what you mean. Thats what I had figured earlier from your comments. If we
are going to make these changes then I would say lets go the full way and make
each test explicitly create the mock task instead of doing it in the setup()
where there is no context. My original change was not good for readability but
was the minimal local change. Your change is good for readability but we are
stopping midway by making future changers have to think on why the reduce test
has been special cased. So IMO lets make each test create mock tasks as
appropriate in context. Its going to be same wrt perf but a lot better to read.
In a sense the original tests were only using mappers and the current setup
method made sense. Introducing reducer tests invalidates that approach. What do
you think?
> 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, MAPREDUCE-4607.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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