neilconway opened a new issue, #21349:
URL: https://github.com/apache/datafusion/issues/21349
### Describe the bug
From the plan for TPC-H Q22, in the #21240 branch:
```
ScalarSubqueryExec: subqueries=1
RepartitionExec: partitioning=RoundRobinBatch(4), input_partitions=1,
maintains_sort_order=true
SortPreservingMergeExec: [cntrycode@0 ASC NULLS LAST]
SortExec: expr=[cntrycode@0 ASC NULLS LAST],
preserve_partitioning=[true]
...
```
EnforceDistribution inserts a RepartitionExec:
partitioning=RoundRobinBatch(N) on an already-sorted single-partition output,
followed immediately by SortPreservingMergeExec to merge them back. This is
wasted work — the data is split and immediately re-merged.
This might be related / subset of #4368, not sure exactly.
### To Reproduce
_No response_
### Expected behavior
_No response_
### Additional context
_No response_
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