Multiple ChoiceHard 45s
Fan-out on write vs read
A news feed precomputes each user's timeline at post time. A celebrity with 100M followers posts. What is the problem?
Options
- 1No fan-out happens at all because the post is only delivered lazily when each individual follower next logs in again
- 2Followers receive the post instantly with no extra write cost because every read is served from a shared cache
- 3The feed becomes strongly consistent, so every one of the followers sees the post in exactly the same global order
- 4A single post triggers 100M write/insert operations (fan-out on write), causing a huge write spike and storage amplification
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