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Designing a Counterfeit & Prohibited Listing Detection System at Scale How marketplaces like Amazon, eBay, Etsy and Flipkart automatically catch fake, stolen, and banned products among millions of new listings every single day — and how to build that system yourself, from first principles. 01 · Intro02 · Problem03 ·…
Designing a System to Detect and Respond to Coordinated Disinformation Campaigns A production-grade architecture for spotting coordinated inauthentic behavior across multiple accounts and platforms in real time — built for the chaos of a fast-moving breaking news event. 01 · Introduction02 · Problem03 · Architecture04 · Internals05 · Advanced06 ·…
Designing a System to Detect and Respond to Coordinated Disinformation Campaigns A production-grade architecture for spotting coordinated inauthentic behavior across multiple accounts and platforms in real time — built for the chaos of a fast-moving breaking news event. 01 · Introduction02 · Problem03 · Architecture04 · Internals05 · Advanced06 ·…
Designing a Compromised Merchant Fraud Detection System How to catch a merchant account that has been hijacked and is being used to push fraudulent transactions at unusually high volume — before it drains real money out of the payment network, and without accidentally freezing a legitimate merchant on their biggest…
Designing a Real-Time Content Moderation Pipeline for Text, Images and Video Every second, someone somewhere is uploading a post, a photo, or a video that should never reach another human’s screen. How do platforms like Facebook, YouTube, and TikTok inspect that content, decide whether it’s safe, and act on it…
Solving the Cold-Start Problem in Recommendation Systems How do you recommend the right content to someone the system has never seen before? This is a complete, from-scratch walkthrough of designing a production-grade cold-start recommendation architecture — covering the algorithms, the services, the databases, the failure modes, and the exact questions…
Designing the Algorithmic Explore Page A ground-up, production-grade blueprint for a discovery feed that surfaces content from accounts a user has never followed — covering candidate generation, ranking, embeddings, feature stores, caching, and the trade-offs real platforms make at massive scale. 01 · Introduction02 · Problem03 · Concepts04 · Architecture05…
Designing a “Close Friends” Selective Content Sharing System A complete, production-grade walkthrough of how to build a social platform feature that lets a user post content visible only to a hand-picked subset of their followers — covering the data model, fan-out strategy, access control, caching, and the scaling decisions that…
A real-time multi-language translation system for posts and comments — built from first principles How do platforms show a post written in Japanese to a reader in Brazil, in Portuguese, within a fraction of a second — and do the same for millions of comments arriving every minute, in over…
A production-grade system-design walkthrough for a real-time checkout cross-sell & upsell recommendation engine at ~1M requests/minute: two-speed architecture (fast cache-driven online path + async Kafka/Flink/warehouse/model-registry offline path), Recommendation Orchestrator with a hard 40 ms timeout budget and static fallback, three-layer caching (edge, in-proc LRU, Redis cluster), Rules Engine as final…