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Design system to detect privacy-leak records

TikTokSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenML System Design

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This question evaluates a candidate's ability to design scalable ML-driven systems for detecting and classifying privacy-sensitive and PII-containing records across structured and unstructured data, testing competencies in data engineering, machine learning (including deep learning and LLM/RAG integrations), system architecture, and privacy/security considerations. It is commonly asked to probe reasoning about functional and non-functional requirements, trade-offs in detection and classification approaches, evaluation metrics like precision and recall, feedback loops and operational scaling, and it falls under ML system design with a practical, application-level focus rather than purely conceptual abstraction.

You are given a very large database that contains user data (both structured fields and unstructured text such as logs, messages, and documents). The company wants to automatically:

  1. Identify records that may contain privacy-sensitive or PII (personally identifiable information), such as names, phone numbers, email addresses, or more subtle leaks (e.g., combinations of attributes that uniquely identify a person).
  2. Classify these records by type and severity of privacy risk.

You may use traditional ML, deep learning, and LLM-based approaches (e.g., retrieval-augmented generation, RAG).

Design an end-to-end system that solves this problem. In your design, describe:

  • Functional and non-functional requirements.
  • High-level architecture and main components.
  • How you detect and classify privacy leaks (including any rule-based, ML, and LLM/RAG parts).
  • How the system scales to large datasets.
  • How you evaluate quality (precision/recall) and build a feedback loop.
  • Any privacy or security concerns in the detection pipeline itself.

Assume the database could have billions of rows, with multiple data sources and schemas.