Design Twitter Timeline
Last updated: June 3, 2026
Quick Overview
Design the architecture for Twitter Timeline. Cover scalability, data storage, caching, and real-time requirements.
Twitter/X
System Design
Software Engineer
Twitter/X
June 3, 2026Software Engineer
Technical Screen
System Design
Easy
4
6
4,616 solved
Design the architecture for Twitter Timeline. Cover scalability, data storage, caching, and real-time requirements.
Twitter/X asks this during the Technical Screen to assess your understanding of the full ML lifecycle. They want to see how you translate a business problem into an ML objective, design the feature pipeline, and plan for model monitoring and retraining.
What the Interviewer Expects
- Map the business problem to a concrete ML objective
- Propose reasonable features and a baseline model
- Discuss basic model evaluation metrics
- Outline a simple serving architecture
Key Topics to Cover
ML objective formulation and metric selection
Feature engineering and feature stores
Online vs offline evaluation
Model serving and latency optimization
Feedback loops and model retraining
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle the cold start problem?
- How would you handle a 10x increase in prediction requests?
- What is your model retraining strategy?
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Requirements
Functional Requirements
- User Timeline: Users should see a personalized timeline of tweets from accounts they follow, sorted by relevance and recency.
- Refresh Mechanism: Timeline should...
Capacity Estimation
Assuming Twitter has around 400 million active users and each user fetches their timeline 10 times a day:
- Total Requests per Day: 400M users * 10 fetches = 4 billion requests per day.
- **Reques...
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