Shopify just did something that would make most engineers do a double-take: they replaced Redis with MySQL for their inventory reservation system, and it scaled better. The story hit 86 points on Hacker News with 48 comments because it challenges one of the most common assumptions in modern backend architecture: if you need fast, high-throughput operations, you need Redis.
As it turns out, you don't always need Redis. Sometimes you need better engineering.
The Problem: Inventory at Shopify Scale
Shopify processes millions of orders per day. Every order involves inventory reservations — temporarily holding stock while a payment is processed, then either committing or releasing the hold. This is the classic "inventory reservation" or "soft hold" pattern that any e-commerce platform needs.
The requirements are brutal:
shopify.engineering
