Design a low-latency Notification System
Last updated: April 6, 2026
Quick Overview
Design a low-latency notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Waymo
System Design
Software Engineer
Waymo
April 6, 2026Software Engineer
System Design Round
System Design
Hard
106
6
432 solved
Design a low-latency notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Waymo asks this during the System Design Round to assess your understanding of the full ML lifecycle. They want to see how you translate a business problem into an ML objective, design the feature pipeline, and plan for model monitoring and retraining.
What the Interviewer Expects
- Design the full ML lifecycle from data collection to model monitoring
- Address cold start, exploration/exploitation, and model freshness
- Discuss multi-objective optimization and ranking systems
- Plan for model debugging, fairness, and bias mitigation
- Design the feature store and training pipeline for scale
- Address model versioning, canary deployments, and rollback strategies
- Discuss the data flywheel and long-term system evolution
Key Topics to Cover
Monitoring and model degradation detection
Model serving and latency optimization
Training pipeline and infrastructure
Model selection and architecture
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 the cold start problem?
- How would you ensure fairness and reduce bias in the model?
- What is your model retraining strategy?
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Requirements
- Functional Requirements:
- Support real-time notifications for various events (e.g., route changes, vehicle status updates) with <100ms latency.
- Ability to handle millions of notification ...
Capacity Estimation
- Assume Waymo has 1 million active users.
- Each user could receive an average of 5 notifications per day. During peak times, let's say this scales to 10 notifications each due to events (e.g., traff...
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