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Implementation details have been anonymized to protect intellectual property. The methodology, metrics, and results are real. For the full technical breakdown, reach out at tomas@omnimetrix.io.
Loop 09: CTE Double-Reference Elimination (Third Pass)
BEFORE
AFTER
Loop 09: CTE Double-Reference Elimination (Third Pass)
What changed
Replaced a GROUP BY aggregation with a window function to eliminate the last CTE double-reference in the query pipeline. A downstream CTE was referenced by two consumers, forcing the database to re-execute the entire upstream chain twice. Adding a window function inside the same CTE collapsed both references into one, removing the need for a separate aggregation step and its associated join.
Why we expected it to work
The same CTE re-execution pattern had already yielded 33.3% and 22.1% gains in Loops 07 and 08. Pipeline analysis confirmed the upstream chain was still being duplicated: 8 table read operations where 4 would suffice, and 5 join operations where 2 were the structural minimum.
Results
| Metric | Before | After | Delta |
|---|---|---|---|
| Mean response time (cold) | 496ms | 451ms | -9.1% |
| Table read operations | 8 | 4 | -50% |
| Join operations | 5 | 2 | -60% |
| Pipeline stages | 210 | 137 | -35% |
Why it worked
Eliminating the double-reference halved the physical table reads and removed three join operators from the execution plan. The window function piggybacks on an existing partition pass, so it adds negligible cost while replacing an entire CTE that required its own GROUP BY, HAVING filter, and join back into the main chain. The gains are smaller than Loops 07-08 because this was the last and least expensive re-execution instance.
Cumulative impact
Original: 1,829ms →After Loop 09: ~500ms (72.7% total reduction)