YOUR BRIEF
What to work through
Work through facebook Live comments as a spoken system design interview. Start by clarifying the scope, sketch a working design and explain the trade-offs behind your choices.
- Post a comment on a live video
- See new comments while watching
- See comments posted before joining
BEFORE YOU START
Constraints to discuss
- Millions of live videos at once, thousands of comments a second on one video
- Availability over consistency: eventual consistency is fine
- A comment reaches viewers in under 200 ms
Need a starting point?
Watch for these common gaps as you prepare:
- Polling for new comments
- Offset pagination over a list that grows while you read it
- One pub/sub channel that every server processes
- Round-robin load balancing that spreads a video’s viewers over every server
- Ignoring disconnections, or replaying unbounded history on reconnect
Why this question is in the collection
These sources connect the problem to company interview reports or preparation guides. They do not guarantee what a company will ask you.