Preventing Black Friday Overselling With a Stock Reservation Data Model

Checkout systems can oversell during high-traffic sales because stock is read and decremented in separate steps, so concurrent buyers can both pass a stock check for the last unit. The article proposes making the availability condition part of an atomic conditional update, which lets the database serialize competing purchases and rejects requests once stock runs out. To avoid both locking inventory for abandoned carts and reopening the overselling gap, it introduces a reservation table with held, committed, and released states plus expiry timestamps. Stock is held when checkout begins, committed on successful payment, and returned to availability when a hold expires or payment fails. A background worker reclaims expired holds and can run concurrently using row locking with SKIP LOCKED.