LLD Masterclass: Designing a Movie Booking System (BookMyShow)

1. Requirements (The Scope)

• Functional:
  • Browse movies by city.
  • Choose a cinema and a showtime.
  • Select seats and pay.
  • Handle seat locking (Temp-hold for 10 mins).
• Non-Functional:
  • High concurrency for popular movies.
  • No double-booking.

2. Entity Identification

• Cinema: Contains multiple screens.
• Show: Mapping of Movie, Screen, and Time.
• Seat: Has a type (Gold, Silver) and Status (Available, Locked, Booked).
• Booking: Represents a successful transaction.
• SearchService: Optimized for city/movie filtering.

3. Handling Seat Concurrency (The "Senior" Part)

When two users click the same seat at the exact same millisecond, how do you handle it?

• Optimistic Locking: Use a version field in the DB.
• Pessimistic Locking: Lock the Seat row in the database while the user is in the payment flow.

4. The State Pattern

Use the State Design Pattern to manage seat lifecycle:

• AvailableState $\rightarrow$ LockedState (User starts checkout).
• LockedState $\rightarrow$ BookedState (Payment success).
• LockedState $\rightarrow$ AvailableState (Timeout or payment fail).

Final Takeaway

BookMyShow is a State Management problem. Using the State pattern shows you can handle complex logic transitions without messy if-else blocks.

Read Next

• LLD Principles: SOLID in Production
• System Design: Designing a Global Distributed Rate Limiter