YOUR BRIEF
What to work through
Work through a flash sale as a spoken system design interview. Start by clarifying the scope, sketch a working design and explain the trade-offs behind your choices.
- View the sale item
- Secure one unit for a limited time while the sale runs
- Pay for a secured unit to complete the purchase
BEFORE YOU START
Constraints to discuss
- Never sell more than the 10,000 units in stock
- Survive tens of millions of users arriving within seconds
- Fair access: bots and fast clicks should not take every unit
- A secured unit that is not paid for goes back on sale
Need a starting point?
Watch for these common gaps as you prepare:
- No reservation step: holding stock inside a database transaction while the payment runs
- Read the stock, then write it, without an atomic step
- Letting every request reach the backend when only 10,000 can buy
- No plan for units whose payment never comes
Why this question is in the collection
These sources connect the problem to company interview reports or preparation guides. They do not guarantee what a company will ask you.