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System Design · E-Commerce & Pricing Designing a Price-Match Guarantee Detection System How to build a system that watches competitor prices around the clock, matches products correctly, and automatically triggers a price match — at the scale of millions of SKUs and thousands of competitor sites. 01 · Intro &…
Designing a Photo-Sharing System That Serves Billions of Images in Under 100 ms, Globally A complete walkthrough of the upload pipeline, image processing, storage tiering, and global CDN architecture behind photo platforms that feel instant no matter where in the world you open them. 01 · Intro & History02 · Problem03…
Designing a System to Handle Lost Payment Confirmation Callbacks What happens when a payment processor successfully charges a customer’s card, but the network drops the confirmation message on its way back to your servers? How do you build a system that guarantees the customer is never charged without getting their…
Designing a Multi-Vendor Marketplace Cart & Checkout System How platforms like Amazon Marketplace, Etsy, Flipkart, and Alibaba let a single shopping cart hold items from dozens of independent sellers — and still check out as one smooth transaction, with split payments, partial-failure handling, and per-vendor fulfilment behind the scenes. 01…
System Design · Social Graphs Designing a Mutual Friends System at Billion-Connection Scale How do you tell two strangers, in under 100 milliseconds, who they both know — when the underlying graph has billions of people and hundreds of billions of edges? This is the full architecture, from adjacency lists…
Designing a Race-Condition-Safe Peer-to-Peer Money Transfer System How to guarantee that a sender with just enough balance for one transfer can never accidentally send money twice, even when two transfers race in at the exact same instant — at a scale of millions of requests per minute. 01 · Intro…
Designing a Multi-Warehouse Order Fulfillment Routing System How large-scale e-commerce platforms decide, in a few hundred milliseconds, which warehouse should ship each order — balancing inventory availability, distance, shipping cost, warehouse load, and business rules — without ever selling something that isn’t actually on a shelf. A full architectural walkthrough…
Detecting Stolen or Copied Listing Images at Marketplace Scale An interview-focused walkthrough of how to catch sellers who copy another seller’s product photos without permission — processing on the order of a million image events per minute, with sub-second per-image scoring and near-zero false accusations. 01 · Intro & History02…
Designing a Marketplace Dispute Resolution System A complete, beginner-to-advanced walkthrough of the least glamorous but most trust-critical system in any marketplace — evidence submission, case tracking, automated resolution, immutable audit trails, and safe money movement — built to gracefully survive a scenario of a million requests per minute during flash…
A deep, interview-focused walkthrough of how to design a marketplace customer service chatbot that answers “Where is my order?”, “Is this in stock?”, and “What is my account balance?” correctly, in under two seconds, at millions of requests per day, with strict per-customer authorization on every single live data fetch.