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Design Google Search

Design a web search engine with crawling, indexing, ranking, and serving components to handle billions of queries per day.

⏱️ Expected Duration: 60 minutes
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Key Topics to Cover

Web CrawlingInverted IndexPageRankQuery ProcessingSpell Correction

💡 Senior Engineer Focus Areas

  • ▸Freshness vs completeness trade-off
  • ▸Personalization
  • ▸Spam detection
  • ▸Query understanding

Recommended Approach

1. Requirements Clarification

  • • Functional requirements: Core features users need
  • • Non-functional requirements: Scale, latency, availability, consistency
  • • Out of scope: What we won't design today
  • • Constraints: Budget, timeline, existing systems

2. Capacity Estimation

  • • Daily/Monthly Active Users
  • • Read/Write ratio estimation
  • • Storage requirements calculation
  • • Bandwidth estimation
  • • Peak load considerations

3. High-Level Design

  • • Main components and their responsibilities
  • • Data flow for primary use cases
  • • API endpoints and contracts
  • • Database schema overview

4. Detailed Component Design

  • • Deep dive into critical components
  • • Database design and scaling strategy
  • • Caching layer architecture
  • • Message queue implementation

5. Bottlenecks & Trade-offs

  • • Identify single points of failure
  • • Discuss CAP theorem trade-offs
  • • Scaling challenges and solutions
  • • Cost optimization opportunities

Clarifying Questions to Ask

Functional

  • • What are the core features we must support?
  • • What user actions are most critical?
  • • Are there any features we should exclude?

Non-Functional

  • • Expected number of users/scale?
  • • Latency requirements?
  • • Availability vs consistency preference?
  • • Any geographic distribution needs?

Related Questions

Senior Insight

Judgment > Diagrams

Candidates often fail by treating system design as "draw a diagram" instead of demonstrating judgment, trade-offs, and real-world reasoning.

How to avoid this

"Explain WHY you chose a specific database or strategy over alternatives."