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+```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
+```
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