I Removed One Line of Django Code and My API Got 95ms Faster

The Problem Tripvento's city-matrix endpoint returns every hotel in a city scored against 14 traveler personas. At 33 cities it felt fast. At 212 cities, with 24,000+ hotels, cold responses were creeping toward 700ms and the payload for a single city had quietly reached 1.8MB. Nothing was broken. No alerts were firing. But I knew what that feeling meant. I was about to hit a wall. Before touching a single line of code, I opened a Django shell and started measuring. Profile First. Fix Second. The biggest mistake I see in performance debugging is jumping straight to solutions. Add an index. Throw in a cache. Upgrade the droplet. All of these can mask the real problem while adding complexity. I isolated each layer independently: import time from hotels.models import StagingHotel, StagingHotelIntent from hotels.serializers import HotelIntentMatrixSerializer from django.db.models import Prefetch # layer 1 raw query start = time.time() qs = list(StagingHotel.