Design BookMyShow / a Ticket Booking System - System Design
“Design BookMyShow” looks like a catalogue app: list cities, list movies, list showtimes, take a payment, print a QR code. The interviewer …
Read MoreDesign Dropbox / a File Sync and Storage Service - System Design
A file sync service sounds like a glorified upload button until you count the bytes. The naive version is a single PUT /file that stores a …
Read MoreDesign Search Autocomplete / Typeahead - System Design
Everyone thinks autocomplete is a LIKE 'prefix%' query. “Index the search terms, run a prefix match, return the top ten, done.” Then the …
Read MoreDesign a Distributed Cache (like Redis) - System Design
Everyone thinks a cache is a hash map with a size cap. “Store key-value pairs in RAM, evict when it fills up, done.” Then the interviewer …
Read MoreDesign a Payment System / Digital Wallet - System Design
“Move 500 rupees from Alice to Bob” sounds like an UPDATE statement. Then you think about it. What if the request times out and the client …
Read MoreDesign Google Docs / Collaborative Editing - System Design
A document editor sounds trivial until you put two people in the same document. One editor is a text box that saves to a database: type, PUT …
Read MoreDesign a Notification System (Push, Email, SMS) - System Design
“Send the user a notification” sounds like one function call. Then you write it down. Which channel - push, email, SMS, in-app? What if the …
Read MoreDesign a Rate Limiter - System Design
Everyone thinks the rate limiter is a for-loop with a counter. “Count requests per user per minute, reject when it goes over 100, done.” …
Read MoreDesign Uber / a Ride-Hailing System - System Design
“Design Uber” sounds like a CRUD app with a map on top. A rider taps a pin, a driver shows up, money moves. The interviewer lets you believe …
Read MoreDesign a URL Shortener (TinyURL) - System Design
Everyone thinks the URL shortener is a trivial problem. “It’s a hash map. Store long URL, return short URL, done.” Then the interviewer …
Read MoreDesign Twitter's News Feed - System Design
The Twitter timeline looks trivial until you say the numbers out loud. “Show me a list of tweets from people I follow, newest first.” It is …
Read MoreDesign WhatsApp / a Chat Messaging System - System Design
A chat app sounds like the easiest system you will ever build. “User A sends a message, user B receives it.” One INSERT, one SELECT. The …
Read MoreThe Real Cost of Running Production Systems
You just shipped a new service. It works. The demo went great. Leadership is happy. Then the bill arrives - not just the AWS invoice, but …
Read MorePostgreSQL Is All You Need (Until It Isn't)
You’re three months into a new project. You have a PostgreSQL database for your core data, Redis for caching, Elasticsearch for search, …
Read MoreSystem Design Roadmap - What to Learn in What Order
You have 47 browser tabs open. One is a YouTube video on consistent hashing. Another is a blog post about CAP theorem. Somewhere in the mix …
Read MoreHow to Integrate the ChatGPT API - A Complete Guide for Developers
You’ve used ChatGPT through the web interface. Now you want to build it into your own app - a customer support bot, a code review tool, a …
Read MoreHow Redis Went from Single-Threaded to 3.5 Million Ops/Sec
“Redis is single-threaded.” You’ve heard this in every system design interview, every blog post, every tech talk. It was true in 2009. It’s …
Read MoreRedis Internals - Clustering, Sentinel, Sharding, and Pipelining Explained
You spin up a single Redis instance, throw your session data in it, and everything works great. Then your app grows. One day Redis goes down …
Read MoreDatabase Ops/Sec and Memory Limits - When to Shard and When Not To
You’re in a system design interview. You say “we’ll use PostgreSQL” and immediately follow it with “and we’ll shard it across 16 nodes.” The …
Read MorePolling vs Long Polling vs WebSockets - When to Use What
You’re building a notification bell. The product team wants it to feel “real-time.” You reach for WebSockets because that’s what every blog …
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