Art of Codeartofcode
Lesson 14 of 15

43. Design Flash-Sale Ticket Booking (Ticketmaster / IRCTC Tatkal)

1
The interview prompt
2
43.1 What do you ask first?
3
43.2 How big is this, really?
4
43.3 What are the doors?
5
43.4 What do we store?
6
43.5 What does the whole system look like?
7
43.6 How does the waiting room work?
8
43.7 How does seat locking work?
9
43.8 How do you rate-limit bots?
10
43.9 How do you keep it fair?
11
43.10 What would you say in the last five minutes?
12
Score yourself
13
Variations to practise
14
Sources
15
Code lab
43. Design Flash-Sale Ticket Booking (Ticketmaster / IRCTC Tatkal)

Sources

3 min read+10 XP

Source notes

  • Ticketmaster on the Taylor Swift Eras Tour presale (November 2022): "3.5 billion total system requests, 4x our previous peak", with bot attacks among the causes; Verified Fan pre-registration. Ticketmaster statement as reported by news outlets, November 2022. Checked 2026-10-08.
  • IRCTC Tatkal booking opens one day before the journey: 10:00 for AC classes and 11:00 for non-AC classes. IRCTC rules as summarised by travel and banking sites. Checked 2026-10-08.
  • Seat holds and conditional updates: see Chapter 17. Payments: Chapter 42. Rate limits and bots: Chapter 25.
  • Crowd size, seat counts, admit rates and bot counts are interview assumptions agreed in Step 1, not figures for any real sale. Arithmetic computed 2026-10-08.
  • Waiting time and admission arithmetic, seat holds with expiry, and bots' share under first-come, per-account limits and a randomised opening window: tested 2026-10-08 (code/ch43_flash_sale.py, all checks pass).