Glossary term
What is Fan-out? Meaning for developers
In System Design
One event/message spread to many recipients. Example: One post → written into 200 followers' feeds.
Learn it properly · System DesignLesson 64: Design a News FeedA hundred million users opening a feed ten times a day, and one celebrity post that must reach fifty million followers. A full news-feed design: fan-out on write vs on read, the hybrid that handles celebrities, feed caches, hydration, ranking, pagination and counters.In Practical Design Problems
Turning one event into many deliveries, like one broadcast into a million notifications.
Learn it properly · Practical Design ProblemsLesson 5: Design a Notification System (In-App, Push, Email)Polling, long polling, server-sent events and WebSockets, fan-out with queues, read state, user settings, retries and removing duplicates.