How would you design Twitter's timeline at scale?

Question

Accepted Answer

## Step 1: Outline use cases and constraints

> Gather requirements and scope the problem. Ask questions to clarify use cases and constraints. Discuss assumptions.

### Use cases

#### We'll scope the problem to handle only the following use cases

* **User** tweets (280 chars + media) with timeline delivery
* **User** reads home timeline (reverse chronological + ranked)
* **User** follows celebrity accounts
* **Service** hybrid fan-out: push for normal, pull for celeb 1M+ followers
* **Service** serves timeline from Redis sorted set + fallback DB

#### Out of scope

* Custom alias validation detail
* Admin dashboard
* OAuth integration

### Constraints and assumptions

#### State assumptions

* 300M users, 100M DAU, 500M tweets/day
* Celebrity fan-out would be 500M*500M impossible — hence pull
* Read 100:1 write, P99 < 200ms

#### Calculate usage

**Clarify with your interviewer if you should run back-of-the-envelope usage calculations.**

| id | 8 bytes | PK |
| payload | ~1KB | — |

How would you design Twitter's timeline at scale?

Understand the problem

Attempt it yourself

Study the solution

Step 1: Outline use cases and constraints

Use cases

We'll scope the problem to handle only the following use cases

Solution ready — 2 min read

Join the discussion

Discussion (0)

KEEP THE
STREAK ALIVE.

Understand the problem

Attempt it yourself

Study the solution

Step 1: Outline use cases and constraints

Use cases

We'll scope the problem to handle only the following use cases

Solution ready — 2 min read

Join the discussion

Discussion (0)

KEEP THESTREAK ALIVE.

KEEP THE
STREAK ALIVE.