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Designing Message Edit & Delete Consistency for Offline Recipients How messaging platforms guarantee that every recipient — online right now or reconnecting three days from now — converges on the exact same final view of a conversation, even after edits and deletions happen mid-flight. 01 · Intro & History02 ·…
Designing a System to Absorb Massive Meeting-Creation Surges in Video Conferencing Platforms A production-grade deep dive into handling synchronized-timezone traffic spikes — the “9 AM problem” — for systems like Zoom, Google Meet, and Microsoft Teams. 01 · Intro & History02 · The Problem03 · Architecture04 · Internal Working05 ·…
Designing a Real-Time Currency Hedging Recommendation System How to build a system that watches a company’s international payment exposure and the currency markets simultaneously, and tells a treasury team — continuously, not just once a quarter — exactly how much foreign exchange risk they are carrying and what hedge to…
Designing Typing Indicators & Online Presence at Massive Scale A complete, interview-depth system design walkthrough for building the “is online / is typing” features behind a messaging platform serving hundreds of millions of concurrently connected users — covering persistent connections, TTL-backed presence leases, pub/sub fan-out, and the bounded push-vs-pull trade-offs…
Designing a Real-Time Transaction Laundering Detection System How payment platforms catch merchants that quietly process transactions for undisclosed, higher-risk businesses hiding behind a legitimate storefront — built to run at millions of transactions per minute with sub-200 millisecond added latency on the authorization path. 01 · Intro02 · History03 ·…
Designing a Video Conferencing System for 1,000 Participants A deep, production-grade system design walkthrough covering architecture, media routing, scalability, and reliability — the way it is actually built at companies like Zoom, Google, and Microsoft. 01 · Intro & History02 · Architecture03 · Internals04 · Data Flow05 · Scaling 100006…
Designing a Global VoIP System with Adaptive Call Quality A production deep dive into how platforms like WhatsApp Calling, Zoom, Google Meet, and Discord keep voice conversations clear and low-latency for two people at once — one on gigabit fiber in Tokyo, the other clinging to a shaky rural 3G…
Designing a Chargeback and Dispute Processing System A production-grade, interview-focused deep dive into building a platform that ingests card-network disputes, orchestrates merchant responses, applies reason-code rules, and resolves millions of chargebacks a month — without losing a single case or missing a single deadline. 01 · Introduction02 · Architecture03 ·…
Designing a Real-Time Automated Expense Categorization System A production-grade system design walkthrough for classifying personal finance transactions — groceries, dining, transportation, and beyond — into categories the instant they happen, at the scale of millions of transactions per minute. 01 · Intro & History02 · Architecture03 · Internal Working04 ·…
Designing a Real-Time Currency Exchange Rate System A complete, interview-focused system design walkthrough: how to stream live foreign exchange (FX) rates to a multi-currency trading platform, keeping every rate no more than a few seconds old — even under millions of requests per minute, across millions of concurrent WebSocket clients,…