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https://issues.apache.org/jira/browse/MAPREDUCE-718?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12743076#action_12743076
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Devaraj Das commented on MAPREDUCE-718:
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bq. This will possibly put a lot more load on the JT. Are we confident this
will not impact performance?
I guess you are saying this since the system counters will be passed every
heartbeat. But the number of system counters are very few (and on top of that
we can exactly control which system counters to send if we come down to that).
So hopefully, performance is not an issue. Regarding the computation of
statistics, the statistics today look at progress values, but if we replace
that by the relevant counter value for the respective phase, it shouldn't add
any extra overhead.
> Support for per-phase speculative execution
> -------------------------------------------
>
> Key: MAPREDUCE-718
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-718
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: jobtracker
> Affects Versions: 0.21.0
> Reporter: Devaraj Das
> Fix For: 0.21.0
>
>
> It would be good to have support for per-phase speculative execution where
> the algorithm looks at the current phase of a task, and compares with the
> other tasks in the same phase before deciding to launch a speculative task.
> That would have the following benefits:
> 1) Support for jobs where map tasks progresses jumps from 0% to 100%. This is
> true for some jobs like randomwriter. Today, we would launch speculative
> tasks for such jobs (assuming that the tasks are not making progress). But
> most of them would be unnecessary.
> 2) In reality, for reduces, the three phases are quite different from each
> other, and they take different times too. We should see better results when
> we look at per-phase speculation.
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