zhuqi-lucas commented on PR #24445:
URL: https://github.com/apache/datafusion/pull/24445#issuecomment-5351275370

   On the perf question: `physical_sorted_union_order_by_50_uint64` is the 
shape this touches, and the bot has it at ~10% across three runs on different 
commits:
   
   ```
   82edbc3b   404.4ms -> 368.9ms   1.10
   09d9cd2d   416.0ms -> 369.8ms   1.13
   95cc5360   410.3ms -> 373.9ms   1.10
   ```
   
   The smaller variants move less, which is what the mechanism predicts: more 
columns in the sort order means a larger equivalence group to re-project on 
each rebuild.
   
   The query is not public and I could not reduce it to an MRE, but I should 
also be straight about why its number was so much larger. That codebase 
predates `EnsureRequirements` and still runs `EnforceSorting` six times plus 
`EnforceDistribution` twice, so the projection chain is rebuilt eight times per 
plan rather than once. The saving is per rebuild, so consolidating those passes 
-- which upstream already did -- caps most of it. Quoting 45% here without that 
context was misleading and I will rewrite the description around the numbers 
above.


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