Design a distributed A/B Testing System
Last updated: July 10, 2025
Quick Overview
Design a distributed a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Supabase
System Design
Software Engineer
Supabase
July 10, 2025Software Engineer
System Design Round
System Design
Medium
47
3
3,886 solved
Design a distributed a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Supabase asks this during the System Design Round to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
What the Interviewer Expects
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
Key Topics to Cover
Failure handling and fault tolerance
Requirements gathering and capacity estimation
Message queues and async processing
High-level architecture and component design
Security and authentication
API design and rate limiting
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you optimize costs as the system scales?
- How would you migrate from a monolithic to a microservices architecture?
- What monitoring and alerting would you set up on day one?
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Requirements
Functional Requirements
- User Segmentation: Ability to create and manage user segments for targeted A/B tests.
- Experiment Creation: Users can create and configure experiments, definin...
Capacity Estimation
Back-of-Envelope Calculations
- Expected Daily Traffic: Assume 10 million users with an average of 3 requests per user per day = 30 million requests/day.
- QPS Calculation: 30 million requ...
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