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https://issues.apache.org/jira/browse/HADOOP-3840?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matei Zaharia updated HADOOP-3840:
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Status: Open (was: Patch Available)
> Support pluggable speculative execution
> ---------------------------------------
>
> Key: HADOOP-3840
> URL: https://issues.apache.org/jira/browse/HADOOP-3840
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Reporter: Matei Zaharia
> Assignee: Matei Zaharia
> Priority: Minor
> Attachments: HADOOP-3840-v1.txt, HADOOP-3840-v2.patch
>
>
> HADOOP-3412 introduced an way to plug in a job scheduler for MapReduce.
> However, the job schedulers all use JobInProgress.obtainNewMapTask or
> obtainNewReduceTask to select tasks to run from each job, which uses a
> threshold-based speculative execution algorithm that has several shortcomings
> (see JIRAs about the scheduler not speculating tasks that freeze after having
> 80% progress for example). As a first step towards supporting better
> speculative execution policies while not breaking backwards compatibility, it
> makes sense to make the speculative execution policy pluggable. Luckily this
> is easy - we just need an interface around obtainNewMapTask and
> obtainNewReduceTask. This JIRA suggests adding a TaskSelector abstract class
> which, given a TaskTracker and a JobInProgress, chooses a task to run on the
> tracker. A default implementation that uses the current methods in
> JobInProgress is provided. Both TaskSchedulers in trunk are changed to use
> TaskSelector.
> In addition, there are methods to count how many speculative tasks a job
> needs, since TaskInProgress.hasSpeculative() may not work if we change the
> algorithm for selecting speculative tasks. This count is needed for some
> schedulers, such as a fair scheduler.
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