System design interview question

Design LinkedIn (professional network)

Hard · System design (HLD) · Company tags: LinkedIn

The prompt

"Design LinkedIn. Focus on the professional graph: connections, the degree-of-separation shown on every profile and search result, 'people you may know', and profile search. 1 billion members."

What this round really tests

graph computation at scale. The feed part is a solved problem the candidate may already know. The distinguishing feature is that LinkedIn must answer "how are you connected to this person?" on every single profile view and search result — a shortest-path query on a billion-node graph, at tens of thousands of QPS.

Clarifying questions worth asking

Is the connection graph directed?
How deep do degrees go?
Max connections per member?
Real-time or can degrees be stale?
Does search need to filter by degree?
Feed?

How the round usually runs

0–5 min: Scoping
5–10 min: Estimates
10–18 min: Graph storage
18–32 min: Deep dive
32–40 min: Deep dive
40–45 min: Wrap

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