You are designing a personal finance service like Mint.com that connects to users' bank accounts, automatically pulls transactions daily, categorizes spending, and alerts users when they approach their budget limits. The system has 10 million users generating 5 billion transactions per month. Explain your architecture, how you handle the write-heavy transaction ingestion pipeline, your categorization approach, and how budget notifications work.
How to approach it
- Hint 1
This is a write-heavy system (10:1 write-to-read ratio) -- the ingestion pipeline is the hardest part.
- Hint 2
Transaction extraction from banks is slow and unreliable. Use asynchronous processing with a message queue.
- Hint 3
For categorization, think about mapping sellers to categories. 50,000 sellers at ~255 bytes each is only ~12 MB -- fits in memory.
Ready to answer it out loud?
Record your answer in 1:30 and Preptile scores it 1–10 with specifics — what landed, what you skipped, and what to say next time.
Practising needs an invite code. Join the waitlist and we’ll send you one.