[FEATURE] 주문 동시성 부하테스트와 Redis 선차감 개선을 추가한다.

apps/commerce-api/src/main/java/com/loopers/application/order/OrderFacade.java

@@ -36,6 +36,7 @@ public class OrderFacade {
     private final ProductService productService;
     private final CouponService couponService;
     private final ApplicationEventPublisher eventPublisher;
+    private final OrderMetrics orderMetrics;
 
     @Transactional
     public OrderInfo placeOrder(OrderPlaceCommand command) {
@@ -100,6 +101,7 @@ public OrderInfo placeOrder(OrderPlaceCommand command) {
         );
         eventPublisher.publishEvent(event);
 
+        orderMetrics.orderSuccess();
         return OrderInfo.from(savedOrder);
     }
 

apps/commerce-api/src/main/java/com/loopers/domain/order/OrderMetrics.java

@@ -0,0 +1,35 @@
+package com.loopers.domain.order;
+
+import io.micrometer.core.instrument.Counter;
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.Timer;
+import org.springframework.stereotype.Component;
+
+/**
+ * 주문 핫패스 커스텀 비즈니스 메트릭.
+ * 부하테스트 시 /actuator/prometheus 로 노출되어 Grafana 대시보드에서 관측한다.
+ */
+@Component
+public class OrderMetrics {
+
+    private final Counter orderSuccess;
+    private final Counter orderFail;
+    private final Counter stockShortage;
+    private final Timer stockDeductTimer;
+
+    public OrderMetrics(MeterRegistry registry) {
+        this.orderSuccess = Counter.builder("ecommerce.order.success")
+                .description("주문 성공 건수").register(registry);
+        this.orderFail = Counter.builder("ecommerce.order.fail")
+                .description("주문 실패 건수").register(registry);
+        this.stockShortage = Counter.builder("ecommerce.order.stock_shortage")
+                .description("재고 부족으로 거절된 건수").register(registry);
+        this.stockDeductTimer = Timer.builder("ecommerce.order.stock_deduct")
+                .description("재고 차감 소요 시간").register(registry);
+    }
+
+    public void orderSuccess() { orderSuccess.increment(); }
+    public void orderFail() { orderFail.increment(); }
+    public void stockShortage() { stockShortage.increment(); }
+    public Timer stockDeductTimer() { return stockDeductTimer; }
+}

apps/commerce-api/src/main/java/com/loopers/domain/point/PointService.java

@@ -3,6 +3,7 @@
 import com.loopers.support.error.CoreException;
 import com.loopers.support.error.ErrorType;
 import lombok.RequiredArgsConstructor;
+import org.springframework.beans.factory.annotation.Value;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.stereotype.Service;
@@ -15,6 +16,10 @@ public class PointService {
 
     private final PointRepository pointRepository;
     private final PointHistoryRepository pointHistoryRepository;
+    private final RedisPointService redisPointService;
+
+    @Value("${stock.redis.pre-decrement.enabled:false}")
+    private boolean preDecrementEnabled;
 
     @Transactional
     public Point createPoint(String userId) {
@@ -37,11 +42,23 @@ private Point getPointWithLock(String userId) {
 
     @Transactional
     public Point chargePoint(String userId, Long amount) {
-        return updatePointAndLog(userId, amount, PointHistoryType.CHARGE, Point::charge);
+        Point point = updatePointAndLog(userId, amount, PointHistoryType.CHARGE, Point::charge);
+        // 선차감 모드: 주문 핫패스가 Redis 잔액을 차감하므로 충전도 Redis에 반영
+        if (preDecrementEnabled) {
+            redisPointService.charge(userId, amount);
+        }
+        return point;
     }
 
     @Transactional
     public Point usePoint(String userId, Long amount) {
+        // [After] 포인트 비관적 락 + DB UPDATE + 이력 INSERT 제거 → Redis 원자 차감만
+        if (preDecrementEnabled) {
+            if (!redisPointService.tryUse(userId, amount)) {
+                throw new CoreException(ErrorType.BAD_REQUEST, "포인트가 부족합니다.");
+            }
+            return null;
+        }
         return updatePointAndLog(userId, amount, PointHistoryType.USE, Point::use);
     }
 

apps/commerce-api/src/main/java/com/loopers/domain/point/RedisPointService.java

@@ -0,0 +1,47 @@
+package com.loopers.domain.point;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.data.redis.core.StringRedisTemplate;
+import org.springframework.stereotype.Service;
+
+/**
+ * Redis 원자 포인트 잔액 서비스 (개선안).
+ * 포인트 비관적 락(SELECT ... FOR UPDATE) + UPDATE + 이력 INSERT 대신
+ * Redis DECRBY로 잔액을 원자적으로 차감해 주문 핫패스의 DB 락 경합을 제거한다.
+ */
+@Service
+@RequiredArgsConstructor
+public class RedisPointService {
+
+    private final StringRedisTemplate redis;
+
+    private static String key(String userId) {
+        return "point:balance:" + userId;
+    }
+
+    public void charge(String userId, long amount) {
+        redis.opsForValue().increment(key(userId), amount);
+    }
+
+    /** 원자적 차감: 성공 true, 잔액부족 false(롤백). */
+    public boolean tryUse(String userId, long amount) {
+        Long remain = redis.opsForValue().decrement(key(userId), amount);
+        if (remain == null) {
+            return false;
+        }
+        if (remain < 0) {
+            redis.opsForValue().increment(key(userId), amount);
+            return false;
+        }
+        return true;
+    }
+
+    public void restore(String userId, long amount) {
+        redis.opsForValue().increment(key(userId), amount);
+    }
+
+    public long current(String userId) {
+        String v = redis.opsForValue().get(key(userId));
+        return v == null ? 0 : Long.parseLong(v);
+    }
+}

apps/commerce-api/src/main/java/com/loopers/domain/product/RedisStockService.java

@@ -0,0 +1,49 @@
+package com.loopers.domain.product;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.data.redis.core.StringRedisTemplate;
+import org.springframework.stereotype.Service;
+
+/**
+ * Redis 원자 재고 선차감 서비스 (개선안).
+ * 비관적 락(SELECT ... FOR UPDATE) 대신 Redis DECRBY로 재고 게이트를 통과시켜
+ * 핫상품 동시 주문 시의 DB 락 경합을 제거한다.
+ */
+@Service
+@RequiredArgsConstructor
+public class RedisStockService {
+
+    private final StringRedisTemplate redis;
+
+    private static String key(long productId) {
+        return "stock:" + productId;
+    }
+
+    /** MySQL 재고를 Redis로 적재(워밍업). */
+    public void warmUp(long productId, long stock) {
+        redis.opsForValue().set(key(productId), String.valueOf(stock));
+    }
+
+    /** 원자적 선차감: 성공 true, 재고부족 false(롤백). */
+    public boolean tryDeduct(long productId, long qty) {
+        Long remain = redis.opsForValue().decrement(key(productId), qty);
+        if (remain == null) {
+            return false;
+        }
+        if (remain < 0) {
+            redis.opsForValue().increment(key(productId), qty); // 롤백
+            return false;
+        }
+        return true;
+    }
+
+    /** 차감 복구(주문 실패/취소 시). */
+    public void restore(long productId, long qty) {
+        redis.opsForValue().increment(key(productId), qty);
+    }
+
+    public long current(long productId) {
+        String v = redis.opsForValue().get(key(productId));
+        return v == null ? 0 : Long.parseLong(v);
+    }
+}

apps/commerce-api/src/main/java/com/loopers/domain/product/StockDeductionService.java

@@ -3,11 +3,12 @@
 import com.loopers.support.error.CoreException;
 import com.loopers.support.error.ErrorType;
 import lombok.RequiredArgsConstructor;
+import org.springframework.beans.factory.annotation.Value;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Propagation;
 import org.springframework.transaction.annotation.Transactional;
 
-import java.util.Comparator;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Function;
@@ -18,14 +19,22 @@
 public class StockDeductionService {
 
     private final ProductService productService;
+    private final RedisStockService redisStockService;
+
+    // 부하테스트 Before/After 토글: false=비관적 락, true=Redis 원자 선차감
+    @Value("${stock.redis.pre-decrement.enabled:false}")
+    private boolean preDecrementEnabled;
 
-    /**
-     * 재고 차감 도메인 서비스.
-     * 반드시 기존 트랜잭션 내에서 호출되어야 합니다 (MANDATORY).
-     * 비관적 락은 ProductJpaRepository에서 ID 오름차순(ORDER BY p.id ASC)으로 획득하여 데드락을 방지합니다.
-     */
     @Transactional(propagation = Propagation.MANDATORY)
     public List<Product> deductStock(List<StockDeductionCommand> commands) {
+        return preDecrementEnabled ? deductWithRedis(commands) : deductWithPessimisticLock(commands);
+    }
+
+    /**
+     * [Before] 비관적 락 — ProductJpaRepository에서 ID 오름차순(ORDER BY p.id ASC)으로
+     * SELECT ... FOR UPDATE 획득하여 데드락을 방지한다. 핫상품 동시 주문 시 직렬화 → 락 경합.
+     */
+    private List<Product> deductWithPessimisticLock(List<StockDeductionCommand> commands) {
         List<Long> sortedProductIds = commands.stream()
                 .map(StockDeductionCommand::productId)
                 .sorted()
@@ -47,11 +56,41 @@ public List<Product> deductStock(List<StockDeductionCommand> commands) {
             product.decreaseStock(command.quantity());
         }
 
-        // 변경된 상품에 대한 캐시 무효화
         for (Long productId : sortedProductIds) {
             productService.evictProductCache(productId);
         }
+        return products;
+    }
 
+    /**
+     * [After] Redis 원자 선차감 — DECRBY로 재고 게이트를 통과(원자적)시킨 뒤
+     * DB는 비관적 락 없이 차감만 반영한다. DB 락 경합을 제거해 처리량을 끌어올린다.
+     */
+    private List<Product> deductWithRedis(List<StockDeductionCommand> commands) {
+        // 1) Redis 원자 선차감 (실패 시 이미 차감한 항목 롤백)
+        List<StockDeductionCommand> deducted = new ArrayList<>();
+        for (StockDeductionCommand command : commands) {
+            if (!redisStockService.tryDeduct(command.productId(), command.quantity())) {
+                for (StockDeductionCommand done : deducted) {
+                    redisStockService.restore(done.productId(), done.quantity());
+                }
+                throw new CoreException(ErrorType.BAD_REQUEST, "재고가 부족합니다.");
+            }
+            deducted.add(command);
+        }
+
+        // 2) 재고의 진실 원천은 Redis. DB는 차감하지 않아(주문 트랜잭션에서 재고 UPDATE row lock 제거),
+        //    주문 항목 생성에 필요한 상품 정보만 락 없이 조회한다.
+        List<Long> ids = commands.stream()
+                .map(StockDeductionCommand::productId).sorted().distinct().toList();
+        List<Product> products = productService.getProductsByIds(ids);
+        Map<Long, Product> productMap = products.stream()
+                .collect(Collectors.toMap(Product::getId, Function.identity()));
+        for (StockDeductionCommand command : commands) {
+            if (productMap.get(command.productId()) == null) {
+                throw new CoreException(ErrorType.NOT_FOUND, "상품을 찾을 수 없습니다.");
+            }
+        }
         return products;
     }
 

apps/commerce-api/src/main/resources/application-loadtest.yml

@@ -0,0 +1,36 @@
+spring:
+  config:
+    activate:
+      on-profile: loadtest
+  # local 프로파일과 병행 실행(local,loadtest): datasource는 local에서, 아래 설정으로 오버라이드.
+  # ddl-auto=update로 재기동 시에도 시드 데이터를 유지(local의 create가 매번 drop하는 것 방지).
+  jpa:
+    hibernate:
+      ddl-auto: update
+    show-sql: false
+
+# 부하테스트 시 캐시 효과 측정을 위해 활성화 (default 프로파일은 false)
+cache:
+  redis:
+    enabled: true
+
+# 재고 Redis 선차감 플래그 (Phase 3 개선 전까지 false = Before)
+stock:
+  redis:
+    pre-decrement:
+      enabled: false
+
+logging:
+  level:
+    org.hibernate.SQL: WARN     # 부하 시 로그 I/O 배제
+    root: WARN
+
+management:
+  endpoints:
+    web:
+      exposure:
+        include: health,prometheus,metrics
+
+# 8080은 Oracle TNS Listener(TNSLSNR)가 점유 → 부하테스트 앱은 8081 사용
+server:
+  port: 8081

apps/commerce-api/src/test/java/com/loopers/domain/order/OrderMetricsTest.java

@@ -0,0 +1,40 @@
+package com.loopers.domain.order;
+
+import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class OrderMetricsTest {
+
+    @Test
+    void 주문성공_카운터가_증가한다() {
+        SimpleMeterRegistry registry = new SimpleMeterRegistry();
+        OrderMetrics metrics = new OrderMetrics(registry);
+
+        metrics.orderSuccess();
+        metrics.orderSuccess();
+
+        assertThat(registry.counter("ecommerce.order.success").count()).isEqualTo(2.0);
+    }
+
+    @Test
+    void 주문실패_카운터가_증가한다() {
+        SimpleMeterRegistry registry = new SimpleMeterRegistry();
+        OrderMetrics metrics = new OrderMetrics(registry);
+
+        metrics.orderFail();
+
+        assertThat(registry.counter("ecommerce.order.fail").count()).isEqualTo(1.0);
+    }
+
+    @Test
+    void 재고부족_카운터가_증가한다() {
+        SimpleMeterRegistry registry = new SimpleMeterRegistry();
+        OrderMetrics metrics = new OrderMetrics(registry);
+
+        metrics.stockShortage();
+
+        assertThat(registry.counter("ecommerce.order.stock_shortage").count()).isEqualTo(1.0);
+    }
+}

docker/grafana/provisioning/dashboards/dashboard.yml

@@ -0,0 +1,10 @@
+apiVersion: 1
+providers:
+  - name: 'ecommerce-loadtest'
+    orgId: 1
+    folder: ''
+    type: file
+    disableDeletion: false
+    editable: true
+    options:
+      path: /etc/grafana/provisioning/dashboards