Add index on (user_id, shown) in notification table to optimize markNotificationsShown queries and prevent deadlocks. Implement transaction handling in markNotificationsShown method for atomic updates.

backend/migrations/20260118000000-add-notification-user-shown-index.cjs

@@ -0,0 +1,30 @@
+"use strict";
+
+module.exports = {
+  async up(queryInterface, Sequelize) {
+    // Create index on (user_id, shown) to optimize markNotificationsShown queries
+    // This prevents deadlocks by allowing fast lookups and reducing lock contention
+    await queryInterface.sequelize.query(`
+      DO $$
+      BEGIN
+        IF NOT EXISTS (
+          SELECT 1 FROM pg_class c 
+          JOIN pg_namespace n ON n.oid = c.relnamespace
+          WHERE c.relkind = 'i' 
+            AND c.relname = 'idx_notification_user_id_shown' 
+            AND n.nspname = 'falukant_log'
+        ) THEN
+          CREATE INDEX idx_notification_user_id_shown 
+          ON falukant_log.notification (user_id, shown);
+        END IF;
+      END$$;
+    `);
+  },
+
+  async down(queryInterface, Sequelize) {
+    await queryInterface.sequelize.query(`
+      DROP INDEX IF EXISTS falukant_log.idx_notification_user_id_shown;
+    `);
+  }
+};
+

backend/services/falukantService.js

@@ -4382,11 +4382,26 @@ class FalukantService extends BaseService {
 
     async markNotificationsShown(hashedUserId) {
         const user = await getFalukantUserOrFail(hashedUserId);
-        const [count] = await Notification.update(
+        
-            { shown: true },
+        // Use transaction to prevent deadlocks and ensure atomicity
-            { where: { userId: user.id, shown: false } }
+        const transaction = await sequelize.transaction({
-        );
+            isolationLevel: Sequelize.Transaction.ISOLATION_LEVELS.READ_COMMITTED
-        return { updated: count };
+        });
+        
+        try {
+            const [count] = await Notification.update(
+                { shown: true },
+                { 
+                    where: { userId: user.id, shown: false },
+                    transaction
+                }
+            );
+            await transaction.commit();
+            return { updated: count };
+        } catch (error) {
+            await transaction.rollback();
+            throw error;
+        }
     }
 
     async getPoliticalOfficeHolders(hashedUserId) {