Design Stack Overflow
Design a simplified version of Stack Overflow that allows users to post questions, submit answers, upvote/downvote content, and add tags.
Stack Overflow is one of the most widely used question-and-answer platforms for software developers. It enables users to ask technical programming questions, receive answers from the community, and collaboratively improve the quality of information through voting and editing.
Although its popularity has declined since the rise of AI tools like ChatGPT, Stack Overflow remains a valuable resource especially for well-structured, peer-reviewed solutions and niche programming discussions.
Stack Overflow is used daily by:
- Beginners looking to troubleshoot basic issues
- Experienced engineers seeking deeper insights
- Experts sharing best practices and advanced techniques
In this chapter, we will explore the low-level design of stack overflow like system in detail.
Let's start by clarifying the requirements:
1. Clarifying Requirements
Before starting the design, it is important to ask thoughtful questions to uncover hidden assumptions and better define the scope of the system.
Here is an example of how a discussion between the candidate and the interviewer might unfold:
Candidate: Should users be able to comment on both questions and answers? And do we need to support nested comments?
Interviewer: Yes, comments are allowed on both questions and answers. However, to keep things simple, we’ll support only flat (non-nested) comments for now.
Candidate: Do we need to implement a user reputation system that changes based on actions like upvotes, downvotes, and accepted answers?
Interviewer: Yes, users should earn or lose reputation based on votes and whether their answer is accepted. The reputation impact may vary depending on whether the vote is on a question or an answer.
Candidate: Should we support features like tagging, searching, and filtering based on tags or keywords?
Interviewer: Yes. Each question can have one or more tags, and the system should support keyword-based search and tag-based filtering.
After gathering the details, we can summarize the key system requirements.
1.1 Functional Requirements
- Users can post questions, answers, and comments on both questions and answers
- Users can upvote or downvote questions and answers. A user can only vote once per post.
- The original poster of a question can accept one answer as the solution.
- Question can have one or more tags
- Users earn or lose reputation points based on upvotes/downvotes on their content and whether their answer is accepted
- Support searching for questions by keywords in the title or body and filtering questions by tags
1.2 Non-Functional Requirements
- Consistency: Voting actions and reputation updates should be strongly consistent and reflected immediately.
- Concurrency: The system must gracefully handle high-concurrency scenarios, such as multiple users voting on the same post simultaneously.
- Scalability: The design should be scalable to accommodate a growing number of users, questions, and answers.