9 min read A/B Experiment System: Low-Level Design An A/B experiment system assigns users to treatment groups, measures whether a metric changes between […] Read article
10 min read Cost Allocation System: Low-Level Design A cost allocation system attributes infrastructure spend to the teams, products, or customers that generated Read article
8 min read A webhook delivery system pushes event notifications to customer-configured HTTP endpoints — the foundation of Stripe, GitHub, Shopify, and Twilio’s Read article
9 min read A cursor-based incremental sync system lets clients efficiently download only the data that has changed since their last sync, rather Read article
10 min read GDPR Article 17 grants users the “right to erasure” — the ability to request that all their personal data be Read article
8 min read A bookmark (save) system lets users collect and organize content they want to revisit — articles, products, listings, posts. Core Read article
9 min read A poll system lets users create questions with multiple choice answers, vote on them, and see real-time results. Used in Read article
9 min read A referral tracking system attributes new user signups to the existing user who referred them, enabling reward programs and measuring Read article
8 min read An idempotency key service ensures that retried API requests do not cause duplicate side effects — a critical requirement for Read article
9 min read A content reporting and abuse detection system allows users to flag harmful content — spam, harassment, hate speech, illegal material Read article
10 min read A content tagging system lets users and systems attach descriptive labels to content — blog posts, products, images, videos — Read article
9 min read Cache warming ensures a cache is pre-populated with frequently accessed data before users experience cache misses. Without warming, a fresh Read article
9 min read A data archival system moves aged, infrequently accessed data from hot storage (fast, expensive) to warm or cold tiers (slower, Read article
10 min read Multi-factor authentication (MFA) adds a second verification layer beyond passwords — protecting accounts even when passwords are compromised. The three Read article
9 min read A follower graph stores directed relationships between users — Alice follows Bob, but Bob may not follow Alice. It powers Read article
