Shopify replaced Redis with MySQL for inventory reservations–and it scaled

Shopify replaced Redis with MySQL for its inventory reservation system by using MySQL 8's SKIP LOCKED feature with a one-row-per-unit design instead of the previous single-row-with-quantity approach. The new system successfully handled record peak traffic during Black Friday 2025 ($5.1 million in sales per minute) while maintaining ACID guarantees and preventing both overselling and underselling. The key learning was that the actual bottleneck differed from what was initially observed and measured, requiring deeper investigation beyond database design choices.