Problem Understanding
Restate the problem in your own words.
Design Reddit (Community Feed + Q&A)
Design a Reddit-class community feed: users post to subreddits, vote on posts and comments, browse subreddit and home feeds ranked by hot / new / top / rising, and read threaded comments to any depth. Moderators run their own subreddits with custom rules + automod. The architecture must rank fast (hot stories rise in minutes), handle viral posts (10 M views / hour), keep comment trees responsive on 10 k-comment threads, and support full-text search across petabytes of content. The decisive trade-offs are materialised vs compute-on-read feed, sync vs async hot ranking, and nested-set vs adjacency-list comment trees.
- RedditThe category-defining community feed; ~500 M MAU; subreddit-first model.
- Hacker NewsTech-focused, single global feed (no subreddits); simpler shape but same ranking ideas.
- Quora / Stack OverflowQ&A-first with reputation systems; comment trees are flatter.
- Lemmy / MastodonFederated Reddit / Twitter — adds inter-instance sync but same core feed mechanics.
Your task: read the problem above, then write what the system is, who uses it, the rough scale, and the headline UX expectation — in your own words. Submit for AI review when you're ready.
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