Rich-T-kid opened a new pull request, #27339:
URL: https://github.com/apache/datafusion/pull/27339

   ## Which issue does this PR close?
   
   - Related to #24822.
   
   ## Rationale for this change
   
   After a selective filter, a dictionary group key can still carry values that 
no surviving row references. This experiment compacts those dictionaries before 
aggregation when the value table is larger than the filtered batch.
   
   ## What changes are included in this PR?
   
   Adds a physical expression for dictionary compaction and applies it to 
direct dictionary group keys in partial or single aggregates above filters.
   
   ## What is the testing strategy for this PR?
   
   Local RLE-dictionary ClickBench results were flat: Q36 moved from 123.72 ms 
to 123.53 ms, while Q38 did not meet the compaction threshold. Hosted TPC-H, 
TPC-DS, and partitioned ClickBench results are pending.
   
   ## Are there any user-facing changes?
   
   No.


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