Design a large-scale Messaging Platform
Last updated: February 22, 2026
Quick Overview
Design a distributed messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Visa
System Design
Software Engineer
Visa
February 22, 2026Software Engineer
Onsite
System Design
Hard
50
5
2,275 solved
Design a distributed messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
ML system design at Visa goes beyond model selection. This Onsite question evaluates your ability to design end-to-end ML pipelines, from data collection to model serving, while considering production constraints like latency and reliability.
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
Model selection and architecture
Feature engineering and feature stores
Model serving and latency optimization
Data collection and labeling strategy
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 prediction requests?
- How would you debug a model that works well offline but poorly online?
- What would you do if model performance degrades over time?
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Requirements
Functional Requirements
- Message Sending and Receiving: Users can send and receive messages in real-time.
- Group Messaging: Support for group chats with up to 100 participants.
- **Me...
Capacity Estimation
Assuming Visa's messaging platform scales to 10 million users:
- Message Frequency: Each user sends an average of 10 messages per day.
- Total Messages: 10 million users * 10 messages = 100 mi...
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