Build a Reddit / Hacker News-shaped product: users submit links, comment in threaded discussions, and vote up/down on submissions and comments. Each subreddit (and the front page) renders **hot / top / new / best** listings ranked by a vote-driven formula. The product is read-tail-dominated: a typical session loads ~5 listings before producing a single vote. Voting is the highest-rate write workload; ranking is the largest async pipeline; comment-trees are the trickiest read path.