📝 Problem Description
Design a professional networking platform like LinkedIn. Users create profiles, connect with professionals, share updates, apply for jobs, and receive personalized recommendations. Focus on the social graph, feed, and job matching.
👤 Use Cases
1.
User wants to sends connection request so that 2nd-degree connection becomes 1st
2.
User wants to views feed so that sees posts from network
3.
User wants to searches people so that finds professionals by skills
4.
User wants to applies to job so that application submitted to recruiter
✅ Functional Requirements
- •Professional profiles (work, education, skills)
- •Connection network (1st, 2nd, 3rd degree)
- •News feed with posts and articles
- •Messaging between connections
- •Job listings and applications
- •People search by skills, company, title
- •Recommendations (people, jobs)
⚡ Non-Functional Requirements
- •Feed load < 500ms
- •Connection degree calculation < 100ms
- •Support 800M users
- •99.9% availability
⚠️ Constraints & Assumptions
- •Social graph is complex (billions of edges)
- •Feed must be relevant to professional interests
- •Privacy settings vary by connection degree
📊 Capacity Estimation
👥 Users
800M users, 300M MAU
💾 Storage
10PB (profiles, posts, messages)
⚡ QPS
Feeds: 100K/sec, Searches: 50K/sec
📐 Assumptions
- • 800M registered users
- • 300M monthly active users
- • Average 500 connections per user
- • 100M posts per day
- • 10 feed views per user per day
- • 5% users post daily
💡 Key Concepts
CRITICAL
Social Graph
Connections stored in graph DB for efficient traversal.
CRITICAL
Connection Degrees
1st = direct, 2nd = friend-of-friend, 3rd = 2 hops away.
HIGH
PYMK
People You May Know: recommend based on mutual connections, same company/school.
HIGH
Feed Ranking
ML model ranks posts by relevance, engagement, recency.
💡 Interview Tips
- 💡Start with the social graph and connection model
- 💡Discuss the People You May Know algorithm
- 💡Emphasize the professional context vs Facebook
- 💡Be prepared to discuss job matching and recommendations
- 💡Know the difference between 1st, 2nd, and 3rd degree connections
- 💡Understand the feed algorithm and content ranking