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System Design Interview Guide

A comprehensive guide to answering system design questions with systematic approach, background knowledge, and evaluation criteria.

Purpose​

This guide was created to address three critical needs:

  • I need to systematically approach system design problems: Learn a structured methodology to break down complex system design questions
  • I need to understand what interviewers evaluate: Know the specific criteria and questions interviewers use to assess system design skills
  • I need to build foundational knowledge: Develop the background understanding of databases, architectures, and design patterns required for system design

The goal is to transform system design interviews from overwhelming challenges into structured, manageable problems you can solve systematically.

Background Knowledge to Pursue​

Before diving into system design problems, ensure you have foundational knowledge in these areas:

Database Types & Characteristics​

When to Use:

  • ACID compliance required
  • Complex relationships between entities
  • Structured data with consistent schema
  • Transactional consistency critical

Key Concepts:

  • ACID properties (Atomicity, Consistency, Isolation, Durability)
  • Normalization vs denormalization
  • Indexing strategies
  • Query optimization

Examples: PostgreSQL, MySQL, Oracle

Architecture Patterns​

N-Tier Architecture:

  • Presentation Tier: User interface and user experience
  • Application Tier: Business logic and application processing
  • Data Tier: Database and data storage
  • Benefits: Separation of concerns, scalability, maintainability

Service-Oriented Architecture (SOA):

  • Services communicate via well-defined interfaces
  • Loose coupling between services
  • Reusable business logic
  • Technology agnostic

Microservices:

  • Small, independent services
  • Each service owns its data
  • Decentralized governance
  • Fault isolation

Essential Resources​

System Design Fundamentals:

Database Deep Dives:

Systematic Approach to System Design​

Phase 1: Requirements Gathering (5-10 minutes)​

📋 Requirements Gathering Checklist

  • Clarify functional requirements
  • Understand scale requirements
  • Identify performance requirements
  • Determine cost constraints
  • Establish availability guarantees
  • Define security requirements

Self-Assessment Questions​

Usage Requirements:

  • Who is using the system?
  • How will it be used?
  • What are they trying to accomplish?
  • What data should be returned?
  • What's the interface/API?

Scale Requirements:

  • How many users? (DAU, MAU)
  • How much data? (storage, growth rate)
  • What's the read/write ratio?
  • What are peak vs average loads?

Performance Requirements:

  • How fast? (latency requirements)
  • What's the throughput? (requests per second)
  • What are the SLA targets?

Cost Requirements:

  • Development cost constraints?
  • Maintenance cost preferences?
  • Open source vs commercial solutions?

Availability Guarantees:

  • Do we need to be always up?
  • What's the acceptable downtime?
  • What are the RTO/RPO requirements?

Interviewer Evaluation Criteria​

What Interviewers Look For​

Problem-Solving Approach:

  • Do you ask clarifying questions?
  • Do you break down complex problems systematically?
  • Do you consider multiple approaches?
  • Do you explain your reasoning clearly?

Technical Knowledge:

  • Do you understand different database types and their trade-offs?
  • Can you discuss scalability strategies?
  • Do you understand distributed systems concepts?
  • Can you explain performance implications?

Communication Skills:

  • Do you engage the interviewer like a co-worker?
  • Do you explain trade-offs and implications?
  • Do you use appropriate technical terminology?
  • Do you adapt your explanation to the audience?

Design Thinking:

  • Do you start with simplicity and enhance as needed?
  • Do you consider operational requirements?
  • Do you think about monitoring and debugging?
  • Do you plan for future evolution?

Common Interviewer Questions​

Requirements & Scope:

  • "What assumptions are you making?"
  • "How would you handle [specific edge case]?"
  • "What if the requirements changed to [new requirement]?"
  • "What's your MVP vs full system approach?"

Technical Decisions:

  • "Why did you choose [specific technology]?"
  • "What are the trade-offs of your approach?"
  • "How would you handle [specific failure scenario]?"
  • "What are the bottlenecks in your design?"

Scalability & Performance:

  • "How would this scale to 10x the current load?"
  • "What happens if one component fails?"
  • "How would you optimize for [specific metric]?"
  • "What's your strategy for handling peak loads?"

Operational Concerns:

  • "How would you monitor this system?"
  • "What metrics would you track?"
  • "How would you debug issues in production?"
  • "What's your deployment strategy?"

Example: Inventory Management System​

Requirements Gathering​

Usage:

  • Fulfillment center operators need real-time inventory visibility
  • Managers need reporting and analytics
  • External systems need inventory updates

Scale:

  • 1M+ inventory items across multiple locations
  • 10K+ daily transactions
  • 100+ concurrent users

Performance:

  • less than 100ms response time for inventory lookups
  • 99.9% availability
  • Real-time updates for critical operations

High-Level Design​

Components:

  • Web frontend for operators
  • API gateway for external access
  • Inventory service for business logic
  • Database for persistence
  • Message queue for async processing

Data Flow:

  • Real-time updates via WebSocket
  • Batch processing for analytics
  • Event-driven updates between services

Detailed Design​

Database Choice:

  • Primary: PostgreSQL for transactional consistency
  • Cache: Redis for frequently accessed data
  • Analytics: Columnar database for reporting

Scalability:

  • Horizontal scaling of application servers
  • Database read replicas
  • CDN for static content

Action Items​

This section contains specific action items that readers can take to enhance their understanding or apply the concepts from this post:

  • Study Database Types: Deep dive into relational, NoSQL, and specialized databases, understanding when to use each and their trade-offs
  • Practice Requirements Gathering: Work through 5 different system design problems, focusing on asking the right clarifying questions and understanding scope
  • Build Architecture Knowledge: Study real-world system architectures (Twitter, Netflix, Uber) to understand how companies solve similar problems at scale
  • Practice Trade-off Discussions: Prepare explanations for common design trade-offs (consistency vs availability, performance vs cost, simplicity vs flexibility)

Implementation Notes:

  • Each action item should be specific and measurable with clear deliverables
  • Focus on understanding trade-offs rather than memorizing solutions
  • Practice explaining your reasoning out loud, as communication is crucial
  • Consider different skill levels: beginners should focus on basic concepts, intermediate on trade-offs, advanced on real-world complexity
  • Provide context: these skills directly translate to real-world system design decisions

Conclusion​

System design interviews test your ability to think systematically about complex problems, make informed technical decisions, and communicate your reasoning effectively. By following a structured approach, building foundational knowledge, and practicing trade-off discussions, you can demonstrate the skills companies look for in senior engineering roles.

Remember: The goal isn't to design the perfect system, but to show how you approach complex problems, make reasoned decisions, and communicate effectively with your team.

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