Design comment ranking
Company: Reddit
Role: Machine Learning Engineer
Category: ML System Design
Difficulty: hard
Interview Round: Onsite
Overview: This question evaluates competency in designing large-scale machine learning ranking systems, testing skills such as candidate generation, label and training data strategy, feature engineering across comments/users/posts/viewer context, model architecture and serving, and operational constraints like freshness, cold start, moderation, latency, and reliability. Commonly asked in ML system design interviews, it measures the ability to balance product goals (usefulness and engagement) with constraints and trade-offs; the domain is machine learning system design and it requires both conceptual understanding and practical application.