```mermaid
sequenceDiagram
    participant User
    participant PaymentService
    participant Database
    participant ExternalService

    User->>PaymentService: 결제 요청
    PaymentService->>Database: 트랜잭션 시작
    alt 정상 흐름
        PaymentService->>ExternalService: 결제 처리 요청
        ExternalService-->>PaymentService: 결제 성공
        PaymentService->>Database: 트랜잭션 커밋
    else 외부 실패
        PaymentService->>Database: 트랜잭션 롤백
    else DB 실패
        PaymentService->>Database: 트랜잭션 롤백
    end
```