Art of Codeartofcode
Lesson 11 of 15

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

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

43.10 What would you say in the last five minutes?

3 min read+10 XP

Step 6: Wrap-up (5 minutes)

  • Bottlenecks: seat inventory rows (sections, conditional updates, admit rate) and payment provider throughput (admit rate tuned to it, second provider).
  • Single points of failure: the waiting room (replicated store, or managed service; if it fails, pause admissions rather than open the floodgates).
  • Correctness: conditional holds, expiring holds, idempotent payments, tickets issued only for paid holds.
  • Fairness and abuse: verified accounts, per-account limits, edge bot defences, randomised opening, signed tokens.
  • Rehearsal: load-test the burst and the "everyone refreshes at 9:59" pattern; pre-scale (Chapter 41).
  • Next with more time: dynamic pricing, resale marketplace with price caps, accessibility seating, and group bookings that keep friends together.

Memory code: "Meter the crowd, hold seats briefly, shuffle the rush, and stop the bots at the door."