Removed: the separate Redis cluster that held checkout inventory reservations.
Outcome: one atomic write path instead of two systems to reconcile, one cluster fewer to maintain, and peak 2025 traffic handled after the cutover.
Shopify ran checkout inventory reservations on Redis for years. Reservations and the inventory ledger lived in two different systems, so claiming stock after payment meant updating MySQL and cleaning up Redis without a single atomic step — “overselling (item sold but was never deducted from the ledger) or underselling (item deducted and still marked reserved).” The Redis model also “added the operational cost of a separate cluster to maintain.”
In May 2026 they moved reservations into the same MySQL database as the ledger. They are explicit that Redis handled concurrency, and that earlier MySQL attempts had failed; the published numbers say they hit peak 2025 traffic after the cutover.
Source: Shopify Engineering, We replaced Redis with MySQL for inventory reservations—and it scaled (12 May 2026)