Massive livestream comments
Your task
Design the live-comments/chat system for a massive livestream. A single stream can have 2M concurrent viewers; at peak (a goal, a product reveal) tens of thousands of comments per second are posted, and every viewer wants a live-feeling comment feed. You obviously can't show all comments to everyone, and you must handle spam, slow-mode, and moderation in real time.
It covers
- Hot stream
- Sampling
- Rate limiting