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Paxos·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Apr 2026

Summary

System design round at Paxos for a software engineering role, focused entirely on building a market surveillance platform for financial exchanges. Pretty intense scope for a single session, covering everything from ingestion to customer-facing event delivery.

Questions Asked (1)

Q1

Design an end-to-end market surveillance platform for financial exchanges that ingests trading orders, routes them to detection algorithms based on trader or exchange identity, and surfaces suspected manipulation events to customers.

System DesignAPI & IntegrationsTechnical Trade-offs
Author's notes

This is a meaty one.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scale, then design a high-level architecture with ingestion, routing, detection, and alerting components. Focus on how routing rules are dynamically applied based on trader/exchange identity, and discuss trade-offs in latency, scalability, and accuracy.

Pro tip: Emphasize the need for a rule engine that can be updated in real-time without redeploying, and discuss how to handle false positives to maintain customer trust.

1. Clarify Requirements

Ask about scale (orders per second), latency requirements, types of manipulation to detect, and customer expectations for alerts.

2. High-Level Architecture

Outline components: ingestion layer (e.g., Kafka), routing service, detection algorithms, alerting service, and customer-facing API. Sketch data flow.

3. Routing Mechanism

Design a rule-based router that uses trader/exchange metadata to direct orders to appropriate detection algorithms. Discuss dynamic rule updates.

4. Detection & Alerting

Explain how detection algorithms process orders (e.g., streaming vs batch), and how suspected events are surfaced to customers with context.

5. Trade-offs & Scalability

Discuss trade-offs: latency vs accuracy, cost vs performance. Address scaling, fault tolerance, and data consistency.

Key Points to Mention

  • Use of stream processing (e.g., Kafka, Flink) for real-time ingestion and detection.
  • Dynamic rule engine for routing based on trader/exchange identity, with hot-reload capabilities.
  • Separation of concerns: ingestion, routing, detection, alerting as independent services.
  • Handling false positives and providing explainability for alerts to customers.
  • Scalability and fault tolerance: partitioning, replication, and backpressure.
  • API design for customers to receive alerts and query historical data.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.