[GitHub] spark issue #16620: [SPARK-19263] DAGScheduler should avoid sending conflict...

[jinxing64]

Github user jinxing64 commented on the issue:

    https://github.com/apache/spark/pull/16620
  
    @kayousterhout @squito @markhamstra 
    
    Thanks a lot for for the comments. I've already refined accordingly.
    I still have one concern:
    > If this is a correct description, I’d argue that (5) is the problem: 
that when ShuffleMapTask2 finishes, we should not be updating a bunch of state 
in the DAGScheduler saying that there’s output ready as a result. If I’m 
understanding correctly, there’s a relatively simple fix to this problem: In 
DAGScheduler.scala, in handleTaskCompletion, we should exit (and not update any 
state) when the task is from an earlier stage attempt that’s not the current 
active attempt. This can be done by changing the if-statement on line 1141 to 
include:
    || stageIdToStage(task.stageId).latestInfo.attemptId != task.stageAttemptId
    
    With above, are we ignoring all the results from old stage attempts?
    As @squito mentioned:
    > It also can potentially improve performance, since you may submit 
downstream stages more quickly, rather than waiting for all tasks in the active 
taskset to complete.
    
    Is it maybe beneficial to add up the result from old stage attempts.


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