System designMediumsd-g540

Subject Comment systemLevel Entry–Mid~35 minCommon in Networking & APIs · Concurrency interviewsIndustries Software development, Technology

Question

Design a basic comment system for a blog. Each article can have comments, comments can have one level of replies (a reply to a top-level comment), and the article page shows comments newest-first with pagination. The site is read-heavy — many more views than new comments. Cover the data model, how you load comments for a page, and how you'd keep the read path fast.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.