```mermaid
sequenceDiagram
    participant User
    participant PaymentService
    participant PaymentGateway
    participant Database

    %% Normal Flow
    User->>PaymentService: Initiate Payment
    PaymentService->>Database: Store Transaction
    Database-->>PaymentService: Transaction Stored
    PaymentService->>PaymentGateway: Process Payment
    PaymentGateway-->>PaymentService: Payment Success
    PaymentService->>Database: Update Transaction Status
    Database-->>PaymentService: Transaction Updated
    PaymentService-->>User: Payment Success

    %% External Failure Flow
    User->>PaymentService: Initiate Payment
    PaymentService->>Database: Store Transaction
    Database-->>PaymentService: Transaction Stored
    PaymentService->>PaymentGateway: Process Payment
    PaymentGateway-->>PaymentService: Payment Failure
    PaymentService->>Database: Rollback Transaction
    Database-->>PaymentService: Transaction Rolled Back
    PaymentService-->>User: Payment Failure

    %% DB Failure Flow
    User->>PaymentService: Initiate Payment
    PaymentService->>Database: Store Transaction
    Database-->>PaymentService: Transaction Store Failure
    PaymentService-->>User: Payment Failure

    %% Commit & Rollback
    Note over User, PaymentService: 
    commit --> PaymentService
    rollback --> PaymentService
```