diff --git a/src/main/java/com/ongil/backend/domain/notification/repository/NotificationRepository.java b/src/main/java/com/ongil/backend/domain/notification/repository/NotificationRepository.java
index 0e8ff55..ed20f50 100644
--- a/src/main/java/com/ongil/backend/domain/notification/repository/NotificationRepository.java
+++ b/src/main/java/com/ongil/backend/domain/notification/repository/NotificationRepository.java
@@ -1,8 +1,12 @@
 package com.ongil.backend.domain.notification.repository;
 
+import java.time.LocalDateTime;
 import java.util.List;
 
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Modifying;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.repository.query.Param;
 
 import com.ongil.backend.domain.notification.entity.Notification;
 
@@ -13,4 +17,9 @@ public interface NotificationRepository extends JpaRepository<Notification, Long
 
 	// 해당 사용자의 읽지 않은 알림 개수 조회 (알림 아이콘 뱅지용)
 	long countByUserIdAndIsReadFalse(Long userId);
+
+	// 해당 사용자의 읽지 않은 알림 전체 읽음 처리 (벌크 UPDATE)
+	@Modifying
+	@Query("UPDATE Notification n SET n.isRead = true, n.readAt = :now WHERE n.user.id = :userId AND n.isRead = false")
+	void markAllAsRead(@Param("userId") Long userId, @Param("now") LocalDateTime now);
 }
\ No newline at end of file
diff --git a/src/main/java/com/ongil/backend/domain/notification/service/NotificationService.java b/src/main/java/com/ongil/backend/domain/notification/service/NotificationService.java
index 91ced89..7fa63e3 100644
--- a/src/main/java/com/ongil/backend/domain/notification/service/NotificationService.java
+++ b/src/main/java/com/ongil/backend/domain/notification/service/NotificationService.java
@@ -1,5 +1,6 @@
 package com.ongil.backend.domain.notification.service;
 
+import java.time.LocalDateTime;
 import java.util.List;
 
 import org.springframework.stereotype.Service;
@@ -51,12 +52,9 @@ public void markAsRead(Long userId, Long notificationId) {
 		notification.markAsRead();
 	}
 
-	// 모든 알림 읽음 처리
+	// 모든 알림 읽음 처리 (벌크 UPDATE로 N+1 방지)
 	@Transactional
 	public void markAllAsRead(Long userId) {
-		List<Notification> notifications = notificationRepository
-			.findByUserIdAndIsReadFalseOrderByNotifiedAtDesc(userId);
-
-		notifications.forEach(Notification::markAsRead);
+		notificationRepository.markAllAsRead(userId, LocalDateTime.now());
 	}
 }
diff --git a/src/main/java/com/ongil/backend/domain/notification/service/NotificationSseService.java b/src/main/java/com/ongil/backend/domain/notification/service/NotificationSseService.java
index 5cb4a94..38f427a 100644
--- a/src/main/java/com/ongil/backend/domain/notification/service/NotificationSseService.java
+++ b/src/main/java/com/ongil/backend/domain/notification/service/NotificationSseService.java
@@ -31,19 +31,19 @@ public SseEmitter subscribe(Long userId) {
 		SseEmitter emitter = new SseEmitter(SSE_TIMEOUT);
 		emitters.put(userId, emitter);
 
-		// 연결 종료 시 제거
+		// 연결 종료 시 제거 (value 지정으로 새로 등록된 emitter를 잘못 제거하는 race condition 방지)
 		emitter.onCompletion(() -> {
-			emitters.remove(userId);
+			emitters.remove(userId, emitter);
 			log.info("SSE 연결 종료 - userId: {}", userId);
 		});
 
 		emitter.onTimeout(() -> {
-			emitters.remove(userId);
+			emitters.remove(userId, emitter);
 			log.info("SSE 타임아웃 - userId: {}", userId);
 		});
 
 		emitter.onError(e -> {
-			emitters.remove(userId);
+			emitters.remove(userId, emitter);
 			log.error("SSE 에러 - userId: {}", userId, e);
 		});
 
@@ -53,7 +53,7 @@ public SseEmitter subscribe(Long userId) {
 				.name("connect")
 				.data("SSE 연결 성공"));
 		} catch (IOException e) {
-			emitters.remove(userId);
+			emitters.remove(userId, emitter);
 			log.error("SSE 초기 이벤트 전송 실패 - userId: {}", userId, e);
 		}
 
@@ -76,7 +76,7 @@ public void sendNotification(Long userId, NotificationResponse notification) {
 				.data(notification));
 			log.info("SSE 알림 전송 성공 - userId: {}, notificationId: {}", userId, notification.getNotificationId());
 		} catch (IOException e) {
-			emitters.remove(userId);
+			emitters.remove(userId, emitter);
 			log.error("SSE 알림 전송 실패 - userId: {}", userId, e);
 		}
 	}
diff --git a/src/main/java/com/ongil/backend/domain/pricealert/service/PriceAlertService.java b/src/main/java/com/ongil/backend/domain/pricealert/service/PriceAlertService.java
index a24fc13..75d8ff8 100644
--- a/src/main/java/com/ongil/backend/domain/pricealert/service/PriceAlertService.java
+++ b/src/main/java/com/ongil/backend/domain/pricealert/service/PriceAlertService.java
@@ -1,5 +1,7 @@
 package com.ongil.backend.domain.pricealert.service;
 
+import java.util.List;
+
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -14,6 +16,7 @@
 import com.ongil.backend.domain.user.repository.UserRepository;
 import com.ongil.backend.global.common.exception.EntityNotFoundException;
 import com.ongil.backend.global.common.exception.ErrorCode;
+import com.ongil.backend.global.common.exception.ValidationException;
 
 import lombok.RequiredArgsConstructor;
 
@@ -30,9 +33,15 @@ public class PriceAlertService {
 	 * 사용자가 상품 상세 화면에서 원하는 할인가를 선택하여 DB에 저장
 	 * 실제 알림 발송은 PriceAlertScheduler가 주기적으로 가격을 확인하여 처리
 	 */
+	private static final List<Integer> ALLOWED_DISCOUNT_RATES = List.of(10, 20, 30, 40);
+
 	@Transactional
 	public PriceAlert createOrUpdatePriceAlert(Long userId, PriceAlertRequest request) {
 
+		if (!ALLOWED_DISCOUNT_RATES.contains(request.getDiscountRate())) {
+			throw new ValidationException(ErrorCode.INVALID_DISCOUNT_RATE);
+		}
+
 		User user = userRepository.findById(userId)
 			.orElseThrow(() -> new EntityNotFoundException(ErrorCode.USER_NOT_FOUND));
 
diff --git a/src/main/java/com/ongil/backend/global/common/exception/ErrorCode.java b/src/main/java/com/ongil/backend/global/common/exception/ErrorCode.java
index a73010c..d1dc070 100644
--- a/src/main/java/com/ongil/backend/global/common/exception/ErrorCode.java
+++ b/src/main/java/com/ongil/backend/global/common/exception/ErrorCode.java
@@ -88,6 +88,7 @@ public enum ErrorCode {
 
 	// PRICE_ALERT
 	PRICE_ALERT_NOT_FOUND(HttpStatus.NOT_FOUND, "설정된 가격 알림이 없습니다.", "ALERT-001"),
+	INVALID_DISCOUNT_RATE(HttpStatus.BAD_REQUEST, "할인율은 10, 20, 30, 40 중 하나여야 합니다.", "ALERT-002"),
 
 	// FILE / S3
 	FILE_IS_EMPTY(HttpStatus.BAD_REQUEST, "파일이 비어 있습니다.", "FILE-001"),