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https://issues.apache.org/jira/browse/MAPREDUCE-5110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13632397#comment-13632397
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Karthik Kambatla commented on MAPREDUCE-5110:
---------------------------------------------

Thanks for your response, Arun.

Let me take a step back and explain in detail:

AIC the issue this JIRA address is - "Where possible (i.e., not transient 
network partitions), run a single task attempt for a task when speculation is 
turned off". A JT solution (a.k.a MAPREDUCE-2217) spawns another task attempt, 
but doesn't kill the currently running task before doing so. Through a TT-side 
solution (patch here), one will be able to kill the currently running attempt 
first before spawning another task attempt.

I see your point of avoid-TT-changes-if-possible. I guess the trade-off is 
between marginal increase in TT code complexity (a timeout check and logging 
changes) and running multiple attempts of the task. Given the low cost of the 
fix, I believe we should address this scenario which seems to be far more 
frequent compared to network partitions.
                
> Long task launch delays can lead to multiple parallel attempts of the task
> --------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-5110
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5110
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: tasktracker
>    Affects Versions: 1.1.2
>            Reporter: Karthik Kambatla
>            Assignee: Karthik Kambatla
>         Attachments: expose-mr-5110.patch, mr-5110.patch, mr-5110.patch, 
> mr-5110-tt-only.patch
>
>
> If a task takes too long to launch, the JT expires the task and schedules 
> another attempt. The earlier attempt can start after the later attempt 
> leading to two parallel attempts running at the same time. This is 
> particularly an issue if the user turns off speculation and expects a single 
> attempt of a task to run at any point in time.

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