Design LinkedIn Connections

This lesson designs LinkedIn Connections, the feature that records who is connected to whom. The design has two very different halves: a small write path, which handles invites and accepts, and a very large read path, which answers "is this person my connection?" on almost every page. Every section below belongs to one of those two halves.

1. Problem Definition and Scope

We are designing the backend system for the "Connections" feature on LinkedIn. This system manages the professional social graph, which is the full record of who is connected to whom.