Design Reddit’s Post Ranking · System Design Interview

Design Reddit’s Post RankingDesign how a link-aggregator site orders the posts inside a community: a vote count that changes constantly, a score that decays with age, and comment trees nested arbitrarily deep.What it has to do

A community’s front page is ordered by a score combining votes and how long ago the post was made

A vote changes a post’s score for the voter immediately, and settles for everyone else shortly after

Comments nest to any depth, and can be sorted best, new or top independently of the post ranking

Scale

Communities: 3 million

Votes per day: 800 million

Posts per day: 5 million

Front page reads per day: 3 billion

Out of scope

Moderation queues

Karma and account history

Vote fraud and rate limiting

Practise this challengeAll system design challenges

LetsDiscuss

Loading your session…