December 4, 2024 6:15 PM PST
This document outlines the system design interview focused on implementing real-time comments on Facebook. The discussion covers technical considerations, design choices, and performance challenges.
Interview Details
- Topic: Real Time Comments on Facebook
- Interviewer Level: L6 (Staff)
System Design Discussion
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Real-Time Commenting Requirements:
- Return comments within 30 seconds of submission.
- Consider using Websockets to reduce load from frequent polling.
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Architecture Considerations:
- Shard users to connect to a specific comment service.
- Store comments in memory for faster access.
- Shard comment servers by post to distribute load effectively.
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Server Design:
- All users in a region should connect to a single server.
- Each server should maintain comments for the past day.
- Use a structure like PostID with a list of strings to manage comments.
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Performance Challenges:
- One server may not be sufficient to handle the volume of comments generated in a day.
- Post ID may not be the best method for sharding; alternative sharding strategies should be considered.
- Determine which posts to serve to users based on engagement metrics.
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Loading Strategy:
- Load top commented posts first.
- Consider how users navigate between servers when scrolling through comments.
Interviewee Feedback
- Performance during the interview was not ideal.
- Focused on stateless server design, but struggled with speed during the deep dive discussion.