[Fix] 서버 안정성 개선 - 커넥션 풀, 쿼리 최적화, 트랜잭션 분리, SSE 타임아웃

backend/src/main/java/com/example/Piroin/project/domain/assignment/service/AssignmentService.java

@@ -34,7 +34,6 @@
 
 @Service
 @RequiredArgsConstructor
-@Transactional
 public class AssignmentService {
 
     private final AssignmentRepository assignmentRepository;
@@ -163,6 +162,7 @@ public ModifyAssignmentResponse modifyAssignment(
     }
 
     // 3. 과제 삭제
+    @Transactional
     public DeleteAssignmentResponse deleteAssignment(Integer assignmentId) {
 
         Assignment assignment = assignmentRepository.findById(assignmentId)
@@ -182,6 +182,7 @@ public DeleteAssignmentResponse deleteAssignment(Integer assignmentId) {
     }
 
     // 4-1. 나의 과제 조회 (부원)
+    @Transactional(readOnly = true)
     public GetMyAssignmentsResponse getMyAssignments(
             Long userId,
             String week

backend/src/main/java/com/example/Piroin/project/domain/attendance/repository/AttendanceRepository.java

@@ -55,6 +55,9 @@ Optional<Attendance> findByUserIdAndAttendanceCodeId(
     List<Attendance> findByAttendanceCodeId(Integer id);
 
 
+    @Query("SELECT a.user.id, COUNT(a) FROM Attendance a WHERE a.user.id IN :userIds AND a.status = false GROUP BY a.user.id")
+    List<Object[]> countFailedAttendanceByUserIds(@Param("userIds") List<Long> userIds);
+
     // 특정 날짜에 발급된 출석 코드의 개수를 세는 메서드
     //long countByAttendanceDate(String attendanceDate);
 

backend/src/main/java/com/example/Piroin/project/domain/attendance/service/AttendanceService.java

@@ -64,22 +64,18 @@ public AttendanceCode generateCodeAndCreateAttendances(LocalDate date) { // [수
             throw new IllegalStateException("하루에 최대 3회까지만 출석 코드를 생성할 수 있습니다.");
         }
 
-        // 1-3) 기존 활성화된 코드들 만료 처리
+        // 1-3) 기존 활성화된 코드들 만료 처리 + 보증금 일괄 재계산
         List<AttendanceCode> activeCodes = attendanceCodeRepository.findByIsExpiredFalse();
         for (AttendanceCode activeCode : activeCodes) {
             activeCode.expire();
         }
 
-        for (AttendanceCode activeCode : activeCodes) {
-            activeCode.expire();
-
-            List<Attendance> attendances =
-                    attendanceRepository.findByAttendanceCodeId(activeCode.getId());
-
-            for (Attendance attendance : attendances) {
-                depositService.recalculateDeposit(attendance.getUser().getId());
-            }
-        }
+        List<Long> userIdsToRecalculate = activeCodes.stream()
+                .flatMap(activeCode -> attendanceRepository.findByAttendanceCodeId(activeCode.getId()).stream())
+                .map(attendance -> attendance.getUser().getId())
+                .distinct()
+                .toList();
+        depositService.recalculateDepositBatch(userIdsToRecalculate);
 
 
         // 1-4) 4자리 랜덤 코드 생성 및 차수(Order) 계산
@@ -208,10 +204,12 @@ public String expireActiveAttendanceCode() {
         List<Attendance> absents =
                 attendanceRepository.findByAttendanceCodeIdAndStatusFalse(attendanceCodeId);
 
-        // 4. 결석자 대상 보증금 재계산 (User ID 타입 Integer 반영)
-        for (Attendance attendance : absents) {
-            depositService.recalculateDeposit(attendance.getUser().getId());
-        }
+        // 4. 결석자 대상 보증금 일괄 재계산
+        List<Long> absentUserIds = absents.stream()
+                .map(attendance -> attendance.getUser().getId())
+                .distinct()
+                .toList();
+        depositService.recalculateDepositBatch(absentUserIds);
 
         return "출석 코드가 성공적으로 만료되었습니다.";
     }

backend/src/main/java/com/example/Piroin/project/domain/deposit/repository/DepositRepository.java

@@ -4,11 +4,13 @@
 import com.example.Piroin.project.domain.user.entity.User;
 import org.springframework.data.jpa.repository.JpaRepository;
 
+import java.util.List;
 import java.util.Optional;
 
 public interface DepositRepository extends JpaRepository<Deposit, Long> {
     Optional<Deposit> findByUser(User user);
 
     Optional<Deposit> findByUserId(Long userId);
 
+    List<Deposit> findByUserIdIn(List<Long> userIds);
 }

backend/src/main/java/com/example/Piroin/project/domain/deposit/service/DepositService.java

@@ -15,6 +15,10 @@
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
 @Service
 @RequiredArgsConstructor
 public class DepositService {
@@ -40,6 +44,25 @@ public void recalculateDeposit(Long userId) {
         deposit.updateAttendanceAmount(descentAttendance);
     }
 
+    // 1-1. 여러 유저 보증금 일괄 재계산 (N*3 쿼리 → 3 쿼리)
+    @Transactional
+    public void recalculateDepositBatch(List<Long> userIds) {
+        if (userIds.isEmpty()) return;
+
+        List<Deposit> deposits = depositRepository.findByUserIdIn(userIds);
+        Map<Long, Integer> failCountMap = attendanceRepository.countFailedAttendanceByUserIds(userIds)
+                .stream()
+                .collect(Collectors.toMap(
+                        row -> (Long) row[0],
+                        row -> ((Long) row[1]).intValue()
+                ));
+
+        for (Deposit deposit : deposits) {
+            int failCount = failCountMap.getOrDefault(deposit.getUser().getId(), 0);
+            deposit.updateAttendanceAmount(failCount * ATTENDANCE_PENALTY);
+        }
+    }
+
     // 2. 보증금 조회 로직
     public DepositResponse getMyDeposit(Long userId) {
 

backend/src/main/java/com/example/Piroin/project/domain/question/service/QuestionEventService.java

@@ -12,7 +12,7 @@
 
 @Service
 public class QuestionEventService {
-    private static final long SSE_TIMEOUT_MILLIS = 60L * 60L * 1000L;
+    private static final long SSE_TIMEOUT_MILLIS = 3L * 60L * 1000L;
 
     // sessionId별로 현재 질문방을 보고 있는 SSE 연결들을 보관한다.
     private final Map<Long, List<SseEmitter>> sessionEmitters = new ConcurrentHashMap<>();

backend/src/main/java/com/example/Piroin/project/domain/user/service/AdminUserService.java

@@ -23,6 +23,9 @@
 import org.springframework.transaction.annotation.Transactional;
 
 import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Collectors;
 
 @Service
 @RequiredArgsConstructor
@@ -76,17 +79,17 @@ public UpdateStudentStatusResponse updateStudentWeekStatus(
                 .orElseThrow(() -> new RuntimeException("사용자가 존재하지 않습니다."));
 
         if (request.getAssignments() != null) {
-            for (UpdateStudentStatusRequest.AssignmentStatusRequest dto
-                    : request.getAssignments()) {
+            List<Integer> itemIds = request.getAssignments().stream()
+                    .map(UpdateStudentStatusRequest.AssignmentStatusRequest::getAssignmentItemId)
+                    .toList();
 
-                // 해당 assignmentItem 존재하지 않을 때
-                AssignmentItem assignmentItem =
-                        assignmentItemRepository.findById(dto.getAssignmentItemId())
-                                .orElseThrow(() ->
-                                        new RuntimeException("과제 정보가 존재하지 않습니다.")
-                                );
+            Map<Integer, AssignmentItem> itemMap = assignmentItemRepository.findAllById(itemIds).stream()
+                    .collect(Collectors.toMap(AssignmentItem::getId, item -> item));
+
+            for (UpdateStudentStatusRequest.AssignmentStatusRequest dto : request.getAssignments()) {
+                AssignmentItem assignmentItem = Optional.ofNullable(itemMap.get(dto.getAssignmentItemId()))
+                        .orElseThrow(() -> new RuntimeException("과제 정보가 존재하지 않습니다."));
 
-                // assignmentItem가 userId의 과제가 아닐 경우
                 if (!assignmentItem.getUser().getId().equals(userId)) {
                     throw new RuntimeException("해당 유저의 과제가 아닙니다.");
                 }
@@ -98,16 +101,17 @@ public UpdateStudentStatusResponse updateStudentWeekStatus(
         }
 
         if (request.getAttendances() != null) {
-            for (UpdateStudentStatusRequest.AttendanceStatusRequest dto
-                    : request.getAttendances()) {
+            List<Long> attendanceIds = request.getAttendances().stream()
+                    .map(dto -> dto.getAttendanceId().longValue())
+                    .toList();
+
+            Map<Integer, Attendance> attendanceMap = attendanceRepository.findAllById(attendanceIds).stream()
+                    .collect(Collectors.toMap(Attendance::getId, a -> a));
 
-                Attendance attendance =
-                        attendanceRepository.findById(dto.getAttendanceId())
-                                .orElseThrow(() ->
-                                        new RuntimeException("출석 정보가 존재하지 않습니다.")
-                                );
+            for (UpdateStudentStatusRequest.AttendanceStatusRequest dto : request.getAttendances()) {
+                Attendance attendance = Optional.ofNullable(attendanceMap.get(dto.getAttendanceId()))
+                        .orElseThrow(() -> new RuntimeException("출석 정보가 존재하지 않습니다."));
 
-                // assignmentId가 userId의 것이 아닐 때
                 if (!attendance.getUser().getId().equals(userId)) {
                     throw new RuntimeException("해당 유저의 출석이 아닙니다.");
                 }

backend/src/main/resources/application.yml

@@ -6,6 +6,12 @@ spring:
     username: ${RDS_USERNAME}
     password: ${RDS_PASSWORD}
     driver-class-name: org.postgresql.Driver
+    hikari:
+      maximum-pool-size: 10
+      connection-timeout: 30000
+      idle-timeout: 600000
+      max-lifetime: 1800000
+      leak-detection-threshold: 5000
 
   flyway:
 #    repair-on-migrate: true
@@ -15,6 +21,7 @@ spring:
     hibernate:
       ddl-auto: validate
     show-sql: true
+    open-in-view: false
     properties:
       hibernate:
         format_sql: true

frontend/src/pages/curriculum/CurriculumPage.js

@@ -318,17 +318,12 @@ function SessionForm({ day, week, onClose, onSave }) {
 
 // ── 메인 컴포넌트 ─────────────────────────────────────
 function CurriculumPage() {
-    const [role, setRole] = useState(null);
+    const role = localStorage.getItem('role') || 'MEMBER';
     const [days, setDays] = useState([]);
     const [showForm, setShowForm] = useState(false);
     const [editDay, setEditDay] = useState(null);
     const [createWeek, setCreateWeek] = useState(null);
 
-    useEffect(() => {
-        setRole(localStorage.getItem('role') || 'MEMBER');
-    }, []);
-
-    // if (role === null) return null;
 
     const fetchDays = async () => {
         try {