Architecture & LLD Preview
Money & Ledger Framework
How to approach money/ledger LLD problems — the append-only ledger, integer cents, idempotency keys, and the shared class vocabulary.
Never store balance — derive it by folding an append-only CREDIT/DEBIT ledger; keep every amount as integer cents; key every mutating call with an idempotency key so retries are answered from cache, not re-applied.
Core Design Challenge
"Design a system that moves money between parties. How do you guarantee a retried mutation never double-applies?"
What You'll Learn:
- ✦Double-entry bookkeeping and ledger accuracy rules
- ✦ACID transaction safety, idempotency, and ledger balance consistency
- ✦Optimizing running balance computations for fast queries
- ✦Auditing, logging, and immutable historical records