System design interview question
"On a food delivery app, users can tap 'notify me' on a restaurant that is currently closed or unavailable. When it reopens, everyone who asked should be told. A popular restaurant might have 200,000 people waiting, and it reopens at a predictable time — so 200,000 notifications fire in the same second, and they all open the app at once."
fan-out on a state transition, with a self-inflicted thundering herd. It looks like a small feature and is genuinely subtle: the notification succeeds too well, so the interesting design work is in spreading delivery, deduplicating subscriptions, and ensuring the restaurant is not instantly overwhelmed by the demand you just created.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
Book a free mock interviewAll 132 system design interview questions
System design mock interviews · DSA interview questions · Free mock interview practice · Browse interviewers · Sign in