cloud-fan commented on issue #24892: [SPARK-25341][Core] Support rolling back a 
shuffle map stage and re-generate the shuffle files
URL: https://github.com/apache/spark/pull/24892#issuecomment-519329319
 
 
   The basic assumption of the speculative task is that: the task output is 
deterministic and we can pick the output of any task which completes first.
   
   The assumption is broken with interminate shuffle stage. We shouldn't launch 
speculative task at all for this case, and thus no need to worry about rolling 
back w/ speculative tasks.
   
   I'm curious to see other use cases of always putting task id in shuffle 
block id. But according to my experience, it's hard to push for a feature that 
brings consistent perf overhead in low-level modules like shuffle.

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