Design a high-throughput Payment System
Last updated: October 30, 2025
Quick Overview
Design a high-throughput payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Waymo
October 30, 202517
12
202 solved
Design a high-throughput payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during System Design Round at Waymo. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. Waymo values engineers who can think about scalability from day one.
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 monitoring and alerting would you set up on day one?
- How would you optimize costs as the system scales?
- What happens if one of your database nodes goes down?
- How do you ensure data consistency across multiple services?
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Requirements
- Functional Requirements:
- Support for multiple payment methods (credit cards, digital wallets, etc.).
- Process transactions in real-time with an SLA of < 200ms.
- Handle refunds and char...
Capacity Estimation
- Estimation:
- Assuming Waymo handles 1 million rides per day, each ride generates an average of 5 payment requests (initial payment, tip, adjustments, etc.).
- This results in approximately ...
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