alamb opened a new issue, #10314:
URL: https://github.com/apache/datafusion/issues/10314

   ### Is your feature request related to a problem or challenge?
   
   The `EnforceDistribution` physical optimizer pass in DataFusion in some 
cases will introduce `InterleaveExec` to increase partitioning when data passes 
through a `UnionExec`:
   
   
https://github.com/apache/datafusion/blob/22311835bc1b4bd83b50e1c3875b0e725622b872/datafusion/core/src/physical_optimizer/enforce_distribution.rs#L1196-L1226
   
   Here is what `InterleaveExec` does: 
https://github.com/apache/datafusion/blob/4edbdd7d09d97f361748c086afbd7b3dda972f76/datafusion/physical-plan/src/union.rs#L286-L317
   
   However, this has the potential downside of destroying and pre-existing 
ordering which is sometimes preferable than increasing / improving 
partitionining (e.g. see https://github.com/apache/datafusion/issues/10257 and 
`datafusion.optimizer.prefer_existing_sort` setting)
   
   ### Describe the solution you'd like
   
   _No response_
   
   ### Describe alternatives you've considered
   
   _No response_
   
   ### Additional context
   
   While working on https://github.com/apache/datafusion/pull/10259 
@mustafasrepo and @phillipleblanc  pointed out that config flag 
`prefer_existing_union` was effectively the same as `prefer_existing_sort`


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