Every social network has some notion for friends/followers/connections that defines affinity of one user to another. So, let's design user affinity your social network that operates at scale.
Say, our social network has a notion of follow and every user can follow every other user. The service should answer "people I follow?" and "people following me?" very efficiently.
The problem statement is something to start with, be creative and dive into the product details and add constraints and features you think would be important.
- every user can follow every other user
- there are 50 million people on our social network
- the two queries that need to be efficiently answered are
- people I follow?
- people following me?
- make your high-level components operate with high availability
- ensure that the data in your system is durable, not matter what happens
- define how your system would behave while scaling-up and scaling-down
- make your system cost-effective and provide a justification for the same
- describe how capacity planning helped you made a good design decision
- think about how other services will interact with your service
- ensure the data in your system is never going in an inconsistent state
- ensure your system is free of deadlocks (if applicable)
- ensure that the throughput of your system is not affected by locking, if it does, state how it would affect
Create a design document of this system/feature stating all critical design decisions, tradeoffs, components, services, and communications. Also specify how your system handles at scale, and what will eventually become a chokepoint.
Do not create unnecessary components, just to make design look complicated. A good design is always simple and elegant. A good way to think about it is if you were to create a spearate process/machine/infra for each component and you will have to code it yourself, would you still do it?
To understand the nuances and internals of this system, build a prototype that
- design the database schema to hold this information at scale
- build a small UI prototype allowing user to follow/unfollow other users (optional)
- load test the two queries for large number of connections and measure the performance
This is a recommended tech-stack for building this prototype
| Which | Options |
|---|---|
| Language | Golang, Java, C++ |
| Database | Pick your favourite |
These are the common pitfalls that you should keep in mind while you are building this prototype
- there would be celebrity accounts who has millions of followers
- the worst case of connections is n^2
- schema design
- database sharding
- indexing internals
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This assignment is part of Arpit's System Design Masterclass - A masterclass that helps you become great at designing scalable, fault-tolerant, and highly available systems.