```mermaid
sequenceDiagram
    participant User
    participant PaymentGateway
    participant Database
    opt Successful Transaction
        User->>PaymentGateway: Initiate Payment
        PaymentGateway-->>User: Payment Confirmation
        User->>Database: Update Transaction Record
        Database-->>User: Transaction Updated
        User->>User: Payment Succeeded
    end
    opt External Failure
        User->>PaymentGateway: Initiate Payment
        PaymentGateway-->>User: Payment Error
        User->>User: Payment Failed
    end
    opt DB Failure
        User->>PaymentGateway: Initiate Payment
        PaymentGateway-->>User: Payment Confirmation
        User->>Database: Update Transaction Record
        Database-->>User: DB Error
        User->>PaymentGateway: Cancel Transaction
        PaymentGateway-->>User: Transaction Canceled
    end
    %% Commit and Rollback%%
    Note over User, PaymentGateway: Commit after successful transaction
    Note over User, Database: Rollback on DB failure
```