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Meta·Machine Learning Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Apr 2026

Summary

ML system design round at Meta for an engineer role. Single question, pretty open-ended, focused on building a monitoring system for a fantasy sports app. The scope was broad enough that you could go in a lot of directions, which was both the interesting part and the stressful part.

Questions Asked (1)

Q1

Design an ML monitoring system for a fantasy sports application. Your design should address data drift, model performance degradation, outlier detection, and data quality issues.

System DesignTechnical Trade-offsRoot Cause Analysis
Author's notes

I started with data quality and worked outward, which in retrospect was probably the right call since everything downstream breaks if your inputs are garbage.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the ML use case (e.g., player performance prediction, lineup optimization) and the system's scale. Then structure your answer around a layered monitoring architecture: data quality, drift detection, model performance, and outlier detection, with feedback loops for root cause analysis and automated responses.

Pro tip: Emphasize the importance of establishing baseline metrics and thresholds during model deployment, and discuss how to prioritize alerts to avoid alert fatigue in a high-scale environment like Meta.

1. Clarify Requirements and Scope

Ask questions to understand the ML model's purpose, data sources, update frequency, and business impact. Define what 'degradation' means in this context (e.g., accuracy drop, increased latency).

2. Design Data Quality Monitoring

Outline checks for missing values, schema changes, range violations, and duplicate records. Include data freshness and completeness metrics, and how to handle anomalies.

3. Implement Drift Detection

Describe methods for detecting data drift (e.g., PSI, KL divergence) and concept drift (e.g., ADWIN, page-Hinkley). Specify which features to monitor and how to set thresholds.

4. Monitor Model Performance and Outliers

Define performance metrics (e.g., RMSE, accuracy) and how to track them over time. Explain outlier detection techniques (e.g., isolation forests, z-scores) for predictions and inputs.

5. Establish Alerting and Root Cause Analysis

Design an alerting system with severity levels and automated root cause analysis (e.g., correlation of drift with performance drops). Include dashboards and feedback loops for retraining.

Key Points to Mention

  • Data drift detection methods: PSI, KL divergence, KS test, and their trade-offs.
  • Concept drift handling: adaptive windowing, ensemble methods, and retraining triggers.
  • Model performance metrics: offline vs. online evaluation, and proxy metrics when ground truth is delayed.
  • Outlier detection: statistical methods (z-score, IQR) and ML-based (isolation forest, autoencoders).
  • Data quality dimensions: accuracy, completeness, consistency, timeliness, and validity.
  • Alerting best practices: threshold tuning, alert prioritization, and integration with incident management.

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