sysdesign-newsfeed-fanout

What problem does it solve?

Balance fan-out on write versus merge-on-read for celebrity-scale social feeds. This skill provides a structured approach to deciding when to push posts to all followers versus merging on read to protect latency and resource usage at scale, while ensuring moderation and traceability.

Core Features & Use Cases

• Hybrid fan-out design: combine write-time propagation for small follow graphs with read-time merging for high-followers.
• Inline moderation and bounded materialized feeds: enforce policy checks before materializing feeds and cap per-user feed length.
• Observability plan: monitor p99 latency by follower-graph shape and provide a clear cutover threshold for celebrity accounts.
• Use Case: a post from a Celeb account should bypass aggressive write fan-out and rely on read-time aggregation for their followers.

Quick Start

Provide a baseline social feed design and flag accounts above a follower threshold to switch from fan-out-on-write to merge-on-read.