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From JoshRosen <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-4939] move to next locality when no pen...
Date Tue, 03 Feb 2015 03:26:45 GMT
Github user JoshRosen commented on the pull request:

    https://github.com/apache/spark/pull/3779#issuecomment-72586368
  
    > If we have tasks at some high locality level that cannot be scheduled at their preferred
locality and there are tasks at a lower locality level that can be scheduled, then I guess
we might be concerned about whether scheduling the less-local tasks could rob tasks waiting
at a higher locality level of their opportunity to run. This shouldn't happen, though, since
those tasks will already have been offered those resources and turned them down.
    
    Actually, on reflection, I guess this gets trickier when you have multiple task sets:
in this case, you want to ensure that _all_ unscheduled process-local tasks have turned down
a resource before you allow _any_ node-local task to obtain it.
    
    I'm going to try to trace through the interaction between DAGScheduler and TaskSetManager
to try to understand how we handle this case.


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