Foundation · 2 min
What you need to know
How do ecommerce stores prevent overselling during high traffic?
Stores prevent overselling by checking and reducing available stock in one protected transaction, using reservations where appropriate and making repeated requests idempotent. A displayed count alone is not enough.
What happens when two customers buy the last item simultaneously?
Both requests may read one unit, but the inventory system must allow only one protected decrement or reservation to succeed. The other customer receives an out-of-stock response or an approved alternative.
When should inventory be reserved?
Reserve inventory at the point the merchant is willing to remove it temporarily from sale, often when checkout begins or payment processing starts. Reserving at cart can unfairly block stock unless the business intentionally accepts that rule.
How long should inventory reservations last?
A reservation should last long enough for a normal checkout and payment attempt, with limited extension for a verified in-progress transaction. Set the duration from observed checkout time and scarce-stock fairness, then show any countdown clearly.
What happens when a reserved checkout is abandoned?
When checkout is abandoned and no valid payment remains in progress, the reservation should expire and return stock exactly once. A cleanup process must handle sessions that never send a normal cancellation event.
How should limited-stock product launches be handled?
Queue or rate-limit entry if demand is extreme, enforce per-customer rules, use atomic inventory allocation and communicate stock status honestly. Load-test the entire purchase path and prepare support for ambiguous orders.
A quick store check
Simulate two attempts to buy the final test item and verify that only one succeeds, and every expired reservation returns stock once.
Foundation · 2 min
Frequently asked questions
Does adding an item to cart always reserve it?
Not necessarily. The merchant must define whether reservation begins in cart, checkout or only after payment.
Can stock counts be corrected manually during a launch?
Only through an audited process; uncontrolled edits can create more overselling and hide the original concurrency problem.