Saga vs Two-Phase Commit: Two Ways to Keep a Transaction Consistent Across Services
A checkout flow that reserves inventory, charges a card, and creates a shipment touches three services, each with its own database. If the charge succeeds but the shipment service is down, the order is now paid with no shipment record, and nothing rolled back the inventory reservation either. That’s not an edge case. Any transaction that crosses a service boundary has this failure mode, because there’s no single database transaction wrapping all three writes. ...