Tech LeadTech Lead (8–12 yrs)RedisKafkaSystem DesignMetaTwitterTikTok
News feed / Instagram feed
Compare fan-out on write vs fan-out on read for a social feed.
Answers use simple, clear English.
Quick interview answer
Fan-out on write pushes posts to followers' timelines (fast read, expensive write, bad for celebrities). Fan-out on read pulls recent posts from followees at read time (cheap write, heavier read). Hybrid: fan-out for normal users, pull for celebrities.
Detailed answer
Fan-out on write pushes posts to followers' timelines (fast read, expensive write, bad for celebrities). Fan-out on read pulls recent posts from followees at read time (cheap write, heavier read). Hybrid: fan-out for normal users, pull for celebrities. Cache timelines in Redis/Cassandra; rank with ML asynchronously.
tech-leadarchitect#feed#fanout#cache