What is the 80 20 rule in system design interviews?
In the context of system design interviews, the 80/20 rule (also known as the Pareto Principle) suggests that by focusing on the most critical 20% of the design aspects, you can address 80% of the core requirements and concerns of the system. It’s a guiding principle that helps you optimize your time and energy, ensuring you cover high-impact components that demonstrate your understanding of scalability, reliability, and performance without getting lost in the minutiae.
1. Focus on High-Impact Components
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Core Services and Data Flow
Identifying the crucial services (e.g., user service, data storage, main APIs) often covers a large portion of the interview's scope. If you can articulate how these services communicate, store data, and handle load, you tackle the bulk of what interviewers look for. -
Scaling Strategies
Highlighting methods to handle growth (like caching, sharding, load balancing) shows you’ve thought about real-world production needs. These patterns typically address the biggest bottlenecks in high-traffic systems. -
Critical Non-Functional Requirements
Concentrate on availability, latency, and reliability. Most real-world issues arise when systems fail or slow down under load, so addressing high-impact resilience strategies (e.g., data replication, circuit breakers) covers most of the interview’s reliability concerns.
2. Trade-Off Discussions
- SQL vs. NoSQL
This choice often determines how you partition and scale data, making it a frequent high-impact topic in system design interviews. - Monolith vs. Microservices
Show that you understand how complexity and organizational needs can shape architectural decisions.
3. Avoid Over-Engineering Early On
While details such as advanced caching hierarchies, multi-region active-active failover, or hyper-optimized data pipelines are interesting, they can also be time-consuming. Start by addressing the major functional and non-functional requirements. If you have extra time, then you can dive deeper into these refinements.
4. Communication and Clarity
By focusing on the 20% that yields 80% of the results, you convey clarity and efficiency. Interviewers want to see a concise, yet comprehensive approach—one that prioritizes the most impactful design elements within limited interview time.
5. Examples in Practice
- Scaling a Social Network
First, address the user profile store, friend-graph representation, and feed generation strategies. These are the key areas (the 20%) that affect 80% of your system’s performance and reliability. - Designing a URL Shortener
Concentrate on the database design for URL mapping, hash generation, and load balancing. Other details (like custom analytics, link previews) can be addressed later if time permits.
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