Payments

← Previous Chapter: Part 6: Distributed Locks, Mutex Invariants & Concurrency in Go | Series Hub: System Design Masterclass | Next Chapter: Part 8: Saga Pattern & Distributed Transactions in Go → Prerequisite: Read Part 6: Distributed Locks, Mutex Invariants & Concurrency in Go to understand distributed mutual exclusion, fencing tokens, and storage invariants before engineering exactly-once API deduplication. Answer-first: Idempotency in distributed financial APIs guarantees that duplicate network requests yield identical outcomes without adverse side effects by enforcing client-generated unique idempotency keys, atomic payload fingerprint validation, and state machine deduplication stores. Combining PostgreSQL row locking with Redis short-term TTL deduplication eliminates double-charge race conditions, ensuring sub-50ms exactly-once payment processing semantics under high concurrency. ...

Answer-first: Payment idempotency guarantees that retrying an identical mutating API request produces the exact same side-effect without duplicate charges. The 2027 SOTA standard requires client-generated Idempotency-Keys, SHA-256 request payload fingerprinting to prevent parameter tampering (HTTP 422), Redis atomic distributed leases (SET NX PX), and database-level unique constraints (SQLSTATE 23505) as the infallible ultimate defense. Prerequisite: Solid mastery of distributed transactions, relational database ACID guarantees, Redis atomic commands, and cryptographic hashing algorithms is required for this chapter. ...