Design a Caching Service
Last updated: July 7, 2025
Quick Overview
Design a geo-distributed caching system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Visa
July 7, 202533
15
3,309 solved
Design a geo-distributed caching system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Visa 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
- Drive the design discussion proactively with minimal interviewer guidance
- Perform detailed capacity estimation and use it to inform design decisions
- Design for global scale with multi-region deployment and data consistency
- Deep dive into 2-3 critical components with implementation-level detail
- Address complex trade-offs: CAP theorem, eventual consistency, conflict resolution
- Discuss operational excellence: deployment strategy, chaos engineering, SLOs/SLIs
- Propose a phased rollout plan from MVP to full-scale system
Key Topics to Cover
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 handle a 10x increase in traffic overnight?
- What happens if one of your database nodes goes down?
- How would you handle schema migrations with zero downtime?
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Requirements
Functional Requirements
- Geo-Distributed Caching: The system must allow for caching data across multiple regions to reduce latency for users worldwide.
- Read/Write Operations: Support ...
Capacity Estimation
Estimation for Visa Caching Service
Assuming Visa handles approximately 65,000 transactions per second globally and expects a read-to-write ratio of 100:1, we can estimate:
- **Total Requests per ...
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