Shopify replaced Redis with MySQL for inventory reservations and it held through $5.1M per minute.

Shopify Engineering published how they moved reservations out of a dedicated Redis cluster into the same MySQL database as the inventory ledger, trading a cache for ACID transactions and eliminating the "payment succeeds but inventory isn't claimed" split-brain class entirely. The enabler is MySQL 8's SKIP LOCKED, letting transactions skip locked rows instead of waiting; reservation pools cap at 1,000 rows per item/location. Black Friday 2025 peak of $5.1M in sales per minute, up 11% YoY, with writer CPU under 50% and reader CPU under 16%. The change removed 50% of reads and 33% of transactions from the primary. Deleting a cache tier and getting faster is the kind of result that should make you re-examine your own Redis usage.