Can you explain how that works? With the row-per-item I can see how you’d use locking primitives etc easily to deal with multiple concurrent shopping carts claiming available inventory.. but how does your solution solve contention? There’d need to be some “number of items in inventory” row, wouldn’t there be contention on that?

The point of one row per item is that thousands of concurrent shoppers don’t need to block each other as they can each claim as many free rows as they need for themselves?