adriangb commented on PR #23390:
URL: https://github.com/apache/datafusion/pull/23390#issuecomment-4920862352

   ## Final benchmark picture (head 775c059d88, adaptive targeting on by 
default)
   
   Two runs prove the two halves of the design contract:
   
   **1. Default run (merge-base vs this branch, no memory limit).** With an 
infinite pool the adaptive path derives no target and the normalizer wrapper is 
never installed, so this is a same-code-path regression check:
   
   | suite | main | branch | detail |
   |---|---|---|---|
   | tpch | 760.3ms | 756.8ms | 22/22 no change |
   | tpcds | 10072ms | 10152ms (+0.8%) | 3 faster / 3 slower / 93 no change, 
movers <=1.09x with overlapping error bars |
   | clickbench_partitioned | 19738ms | 19992ms (+1.3%) | 2 faster / 8 slower / 
33 no change; flagged queries have near-identical minimums (e.g. Q29 "1.40x" 
comes from one ±26ms-stddev outlier run, mins 40.7 vs 41.9ms) |
   
   **2. Same-SHA A/B under `DATAFUSION_RUNTIME_MEMORY_LIMIT=2G` (baseline = 
adaptive disabled, changed = default).** This is the regime where adaptive 
activates (derived target ~10.9MiB at 12 partitions):
   
   | suite | adaptive off | adaptive on | detail |
   |---|---|---|---|
   | tpch | 775.7ms | 781.2ms (+0.7%) | 1 slower (Q2, 1.09x) / 21 no change |
   | sort_tpch | 3668ms | 3707ms (+1.0%) | 10/10 comparable queries no change; 
Q3 (VARCHAR-key sort) fails on BOTH sides — pre-existing 2G capacity limit, 
unaffected by this PR |
   | clickbench_partitioned | 30116ms | 30573ms (+1.5%) | 5 faster / 13 slower 
/ 25 no change, movers <=1.16x both directions |
   | external_aggr | 1492.7ms | 1513.3ms | 8/8 no change (its per-query small 
pools fall under the adaptive minimum and keep exact behavior) |
   
   Summary: with no memory limit the feature is provably inert; under a memory 
limit on standard (small-batch) data it costs ~0.7-1.5% total; and for the 
workloads it exists for (`large_values`: 100MB-536MB decoded batches), the 
earlier comments show it turning ResourcesExhausted into completed queries with 
zero configuration.
   
   🤖 Generated with [Claude Code](https://claude.com/claude-code)
   
   https://claude.ai/code/session_01UcPTREZVLXsSZDRCae33gm
   


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