Ticket/Booking System - System Design

CREATED 2021/11/09 19:40

Functional Requirements

 

Infra

Search Service

Ticket Transaction Service

Payment Service

 

Dataflows

Search a movie

zip code (converted to geo hash)

 

Book a ticket

1 Show the map and availability of all the seats in a specific theatre of a cinema

2 Reserve an available seat

3 User has to make the payment in 15 minutes window

4 If success, the booking is completed. Otherwise, the reserved seat is given back to be available again.

 

Give seat back to available again

1 use a message queue (15 minutes delay) + consumer service (deal with seat status)

2 DB lazy loading. where status = available or (status = pending and current_timestamp - modified_time > 15 mins)

 

DB Schema

Movies (movieId, name, startDate)

Cinema (cinemaId, name, zipcode, address, cinemaHalls)

CinemaHall (cinemaHallId, id, cinemaId)

Events (movieId, cinemaHallId, cinemaId, startTime, geoHash, ...)

Tickets (ticketId, eventId, row, column, price, status, creationTime, modifyTime) - strong consistency

Transaction (ticketId, userId, status)

Users (userId, name, phone, email, membership)

 

Sharding

according to geoHash (convert 2 dimensional numbers (Latitude Longtitude) to string format)

 

Failure

What if payment is successful but the ticket server is down?

We need a Transaction manager (a coordinator) to co-ordinate this. Roll back payment or retry update ticket status.

 

2-phase commit

Coordinator -> Participant1 (undo log and redo log) 

                  -> Participant2 

                  -> Participant3 

Prepare -> -> ->

Vote <- <- <-

Decision -> -> ->

ACK <- <- <-

 

Distributed SQL - Leader-follower mode replica (Both DB and Cache)

 

Disaster Recover

stateless service, kafka as distributed log, Transaction coordinate