Design Comment Prediction Ranking System
Company: Reddit
Role: Machine Learning Engineer
Category: ML System Design
Difficulty: medium
Interview Round: Technical Screen
Overview: This question evaluates proficiency in end-to-end machine learning system design for predicting user engagement, specifically the probability of a user commenting given exposure, covering problem formulation, label and feature engineering, model architecture, training and evaluation pipelines, low-latency serving, and operational concerns like monitoring and cold-start. It falls under the ML System Design / Machine Learning Engineering domain and is commonly asked to assess an engineer's ability to build scalable, bias-aware, low-latency ranking signals that integrate into multi-objective recommenders, with a primarily practical system-level focus rather than purely theoretical modeling.