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https://issues.apache.org/jira/browse/MAPREDUCE-5110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13632543#comment-13632543
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Vinod Kumar Vavilapalli commented on MAPREDUCE-5110:
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Trying to understand this, mostly agree with what Arun said. To summarize:
- Strictly guaranteeing serial execution of task attempts is not possible in
general and is a non-requirement
- JT already deals with all kinds of slow-ness with tasks and irrespective of
this patch, clients have to deal with the slowness.
bq. Where possible (i.e., not transient network partitions), run a single task
attempt for a task when speculation is turned off
Seems an arbitrary non-requirement, don't see what we gain from this.
The JIRA started with the above goal which isn't worth pursing from what I see,
but now it seems to have transformed into something more benign. Looked at the
patch. It looks like you want quicker failure when tasks are getting
launched/localized to meet some kind of SLAs? If that is the case, instead of
calling it a 'TT-side implementation', if we call it an aggressive timeout
enforced on TTs for tasks, and make it job-configurable, that should do. Right?
> 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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