StefanRRichter commented on issue #7009: [FLINK-10712] Support to restore state 
when using RestartPipelinedRegionStrategy
URL: https://github.com/apache/flink/pull/7009#issuecomment-452649422
 
 
   I have one more concern that might lead to bugs in a certain corner case. 
What will happen in your change if the task is using operator state, union 
state in particular. In `applyRepartitioner()`, line 363 you can see that all 
operator state is repartitioned if there is one union state. this can already 
be a problem with a union state, but even more if there is a union state and 
some partionable state -  the partitioning for the partitionable state for 
those tasks that are restarted could differ to the partitioning used in the 
original run - some partitions could be dropped or assigned twice by this. I 
think that means we need to change the method to only redistribute the union 
states, and I wonder if even distributioing the union state only for the failed 
task even makes sense. I think we need a testcase for this scenario (operator 
with 1 union and 1 partionable operator state)and I think it might fail as 
described before when we check how the operator state was reassigned after some 
partial recovery. What do you think?

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