Design a Social Graph / Follow Service

Social, Feed & EngagementMediumdesign-social-graph

Design a Social Graph / Follow Service

Design storage and query for follows, friends, and blocks: bidirectional lookups, friends-of-friends traversal, and accounts with a hundred million edges.

Adjacency ListsGraph PartitioningBidirectional IndexesDenormalization

Traffic & Capacity Estimates:

2B users · 200B edges · 500k edge writes/second · friends-of-friends in <100ms

Functional Requirements

•Create and remove directed edges (follow, block, mute) and query both directions.
•Return follower and following lists with stable pagination.
•Answer 'do these two users have a relationship' in a single hop.
•Support second-degree queries (mutual friends, friends-of-friends) for recommendations.

Non-Functional Requirements

•Edge existence check under 5ms at p99 — it is on the permission path for every view.
•An account with 100M followers must not break the storage model for everyone else.
•Blocks must apply immediately and must never be eventually consistent in the permissive direction.

Back-of-the-Envelope Math

200B edges * 40 bytes = 8 TB of raw edge data, doubled for the reverse index.
Friends-of-friends for a user with 1,000 friends who each have 1,000 friends touches 1M edges — it must be precomputed or sampled.

Key Architectural Trade-offs

A dedicated graph database (natural traversals, harder to shard at this scale) vs sharded adjacency lists in a key-value store (scales trivially, multi-hop queries become application code).
Storing both directions of every edge doubles writes and storage, and is what makes 'who follows me' a single read instead of a full scan.
Safety-critical edges (blocks) demand strong consistency; ordinary follows tolerate eventual consistency — mixing the two in one store means the strict path sets the cost.

Click or drag a component onto the canvas, then connect the handles to draw the data flow.

3 nodes · 2 edges

Components · 35

Client & Edge4

Compute & Gateway7

Storage & Caching11

Messaging & Streaming6

Coordination & Ops5

Intelligence2

React Flow