Low Level Design for Twitter System Design

A low-level design of Twitter dives into the details of individual components and functionalities. Here’s a breakdown of some key aspects:

5.1 Data storage:

• User accounts: Store user data like username, email, password (hashed), profile picture, bio, etc. in a relational database like MySQL.
• Tweets: Store tweets in a separate table within the same database, including tweet content, author ID, timestamp, hashtags, mentions, retweets, replies, etc.
• Follow relationships: Use a separate table to map followers and followees, allowing efficient retrieval of user feeds.
• Additional data: Store media assets like images or videos in a dedicated storage system like S3 and reference them in the tweet table.

5.2 Core functionalities:

• Posting a tweet:
  • User submits tweet content through the UI.
  • Server-side validation checks tweet length, media size, and other constraints.
  • Tweet data is stored in the database with relevant associations (hashtags, mentions, replies).
  • Real-time notifications are sent to followers and mentioned users.
• Timeline generation:
  • Retrieve a list of users and hashtags the current user follows.
  • Fetch recent tweets from those users and matching hashtags from the database.
  • Apply algorithms to rank tweets based on relevance, recency, engagement, etc.
  • Cache frequently accessed timelines in Redis for faster delivery.
• Search:
  • User enters keywords or hashtags.
  • Server-side search analyzes tweet content, hashtags, and user metadata.
  • Return relevant tweets based on a ranking algorithm.
• Follow/unfollow:
  • Update the follow relationships table accordingly.
  • Trigger relevant notifications and adjust user timelines dynamically.

5.3 Additional considerations:

• Caching: Use caching mechanisms like Redis to reduce database load for frequently accessed data like user timelines and trending topics.
• Load balancing: Distribute workload across multiple servers to handle high traffic and ensure scalability.
• Database replication: Ensure data redundancy and fault tolerance with database replication techniques.
• Messaging queues: Leverage asynchronous messaging queues for processing tasks like sending notifications or background indexing.
• API design: Develop well-defined APIs for internal communication between different components within the system.

Designing Twitter (or Facebook feed or Facebook search..) is a quite common question that interviewers ask candidates. A lot of candidates get afraid of this round more than the coding round because they don’t get an idea of what topics and tradeoffs they should cover within this limited timeframe.