Interview Simulator · System Design
Design a Multi-Region Payments Ledger
A full 45 minute round, one phase at a time. Each phase has a time budget, follow-up questions from the interviewer, and a checklist for your level. Reveal a phase's model answer whenever you need it; the report shows which phases you earned.
Design the double-entry ledger for a payments company running in two regions. It handles 40 million transactions a day, every transaction balances to the cent, it reconciles daily against bank and processor files, and it keeps an immutable audit trail. Today, fifteen product teams write directly to a shared Postgres database.