Design a Reddit-style ranked feed

Intermediate50 minBuilds Ranked Discussion FeedRead first: 7.2 Read and write patterns, 19.1 Queues, pub/sub and logs, 17.4 Overload, cascades and graceful degradation

STEP 1 OF 12

The brief

You are designing the front page of a discussion site. Each community has a list of posts ranked by votes and age; the site's front page merges the communities a user follows. Users upvote and downvote constantly, and a post that hits the front page can take thousands of votes a minute.

How big it is

Feed reads: 30,000 / second
Votes: 3,000 / second
Communities: about 100,000
Ranking freshness: within a few seconds
p99 goal: under 200 ms

What makes it tricky

Votes concentrate. Most of the 3,000 votes a second land on a few hundred hot posts, so a naive design hammers a few rows.
Rankings change while you read them. Each vote changes a score, and the score changes the order.
Fairness matters. One user gets one vote per post, and coordinated voting rings must not decide what everyone sees.

All changes saved

0 components · 0 connections

A blank canvas. A better system.

Add components from the palette, then drag between them to connect the request and event flow.

React Flow

Design a Reddit-style ranked feed

Intermediate50 minBuilds Ranked Discussion FeedRead first: 7.2 Read and write patterns, 19.1 Queues, pub/sub and logs, 17.4 Overload, cascades and graceful degradation

STEP 1 OF 12

The brief

How big it is

Feed reads: 30,000 / second
Votes: 3,000 / second
Communities: about 100,000
Ranking freshness: within a few seconds
p99 goal: under 200 ms

What makes it tricky

Votes concentrate. Most of the 3,000 votes a second land on a few hundred hot posts, so a naive design hammers a few rows.
Rankings change while you read them. Each vote changes a score, and the score changes the order.
Fairness matters. One user gets one vote per post, and coordinated voting rings must not decide what everyone sees.

All changes saved

0 components · 0 connections

A blank canvas. A better system.

Add components from the palette, then drag between them to connect the request and event flow.

React Flow