Let me rewind to a Tuesday afternoon I’d rather forget. We had a Rails monolith that had grown fat and happy over five years. The dashboard—a beautiful, chart-filled monster—was running a 12-second query every time the CEO clicked “refresh.” Twelve seconds of GROUP BY , COUNT(DISTINCT) , and LEFT JOIN hell across a million-row events table. The CEO didn’t yell. He just stared at the spinning cursor and said, “This used to be fast.” That silence was worse. I’d already tried everything. Redis caching? Stale data on first load. Counter caches? Fine for counts, useless for complex rollups. Pagination? The dashboard needed totals. I was staring at the ceiling at 2 AM when I whispered: “What if I just… precompute the answer?” Materialized views and summary tables aren’t new. They’re as old as data warehouses. But in Rails, with ActiveRecord’s object‑relational map guiding our every thought, we forget that the database itself can be a cache . A smart, transactional, ACID‑compliant cache that never lies.…