Booking and Search
Selling the same seat to exactly one person, and finding things fast once you have a crore of them.
Design BookMyShow / IRCTC (Seat Reservation)
One seat, two hopeful people, a payment in the middle and a clock running. How to sell every seat exactly once when a lakh of people hit Buy at 10:00 AM, and what to do when the money arrives after the hold has gone.
Seat Hold Simulator
Hold a Tatkal berth in an in-memory Redis simulator, let holds expire mid-payment, race a rival booking agent, and simulate server crashes. Compare Production architecture against the Naive lock implementation to observe the exact race conditions that cause double-booking.
Redis and Search Command Reference
A hands-on lab for the moment a Tatkal or movie-ticket sale opens. You hold seats with Redis, push changes to browsers, run a waiting room, and then search the shows with Elasticsearch. Every command is copy-paste ready.
Search From the Ground Up
Why LIKE '%word%' dies at scale, what an inverted index really is, how text becomes tokens, how shards answer one query together, and a lab you can run on your laptop. Written around Flipkart, Zomato, IRCTC and Swiggy style search boxes.
API Styles, One Food Order
One biryani order, five API styles. REST places it, GraphQL draws the menu, a socket tracks the rider, a webhook confirms the payment, and a session remembers who you are. Click through each one and see where it breaks.