System Design · advanced
Booking & Inventory
Reservation, hold-confirm, optimistic locking.
Mental model
Booking systems are about "holds" — a reservation is itself a write that blocks other people. Pick aggressive hold expirations, treat overbooking as a business policy (not a bug), and choose optimistic vs pessimistic locking based on how often collisions actually happen.
How to study Booking & Inventory
Begin by restating the mental model in your own words, then connect it to a concrete system you have built or operated. Name the mechanism, the constraint it addresses, and the trade-off it introduces. Use System Design Primer, Shopify — Scaling inventory reservations, Optimistic Offline Lock (Fowler, PoEAA catalog) to check details, but close the source before writing your explanation. Retrieval is the learning step; rereading is only preparation.
Next, compare Booking & Inventory with the neighboring concepts in its roadmap. Ask what changes in correctness, latency, resource use, operability, and failure recovery. Complete Hotel booking system and preserve the command, input, output, and one failed attempt as evidence. Finish by explaining the idea without jargon to someone who has not studied the track.
Proof of understanding
- Explain the mechanism from first principles and identify the state it reads or changes.
- Give one situation where the concept is the right choice and one where it is not.
- Predict a realistic failure mode before running the drill, then compare the prediction with evidence.
- Connect the result to a roadmap or build artifact instead of treating the concept as isolated trivia.
Learn from primary sources
Practice and explain it back
Hotel booking system
Design a hotel-room booking system: search availability for a date range, hold a room during checkout, finalize the reservation. Address concurrent bookers fighting for the last room.
Expected evidence: Inventory model + hold/confirm flow + the consistency strategy (optimistic vs pessimistic).
Open the interactive drill →Review prompts
- When should a booking flow take a pessimistic lock instead of an optimistic version check?
Build evidence
Use a roadmap capstone to turn this concept into working evidence.
Prerequisites
Related concepts
None assigned yet.