```mermaid
sequenceDiagram
    participant User as 유저
    participant PaymentService as 결제 서비스
    participant PaymentGateway as 결제 게이트웨이
    participant Database as 데이터베이스

    User->>PaymentService: 결제 요청
    PaymentService->>Database: 결제 정보 저장
    activate Database
    Database-->>PaymentService: 저장 완료
    deactivate Database

    alt 정상 흐름
        PaymentService->>PaymentGateway: 결제 요청
        activate PaymentGateway
        PaymentGateway-->>PaymentService: 결제 성공
        deactivate PaymentGateway
        PaymentService->>User: 결제 완료

    else 외부 실패
        PaymentService->>PaymentGateway: 결제 요청
        activate PaymentGateway
        PaymentGateway-->>PaymentService: 결제 실패
        deactivate PaymentGateway
        PaymentService->>Database: 롤백
        activate Database
        Database-->>PaymentService: 롤백 완료
        deactivate Database
        PaymentService->>User: 결제 실패
    end

    else DB 실패
        PaymentService->>Database: 결제 정보 저장
        activate Database
        Database-->>PaymentService: 저장 실패
        deactivate Database
        PaymentService->>User: 저장 실패
    end
```