Design a Logging for PlanetScale
Last updated: May 1, 2026
Quick Overview
Design a high-throughput logging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
PlanetScale
May 1, 2026427
13
3,468 solved
Design a high-throughput logging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
PlanetScale asks this during the Onsite 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
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
- What happens if one of your database nodes goes down?
- How would you handle schema migrations with zero downtime?
- What would the deployment pipeline look like for this system?
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Requirements
Functional Requirements
- High Throughput: The system should handle millions of log requests per second (QPS).
- Real-Time Processing: Logs should be processed in real-time for immediate...
Capacity Estimation
Assuming PlanetScale serves millions of users and each user generates about 100 logs per minute:
- Estimated QPS:
- 10 million users * 100 logs/user/minute = 1 billion logs/minute = 16.67 milli...
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