diff --git a/dao/src/main/java/org/thingsboard/server/dao/sql/notification/JpaNotificationDao.java b/dao/src/main/java/org/thingsboard/server/dao/sql/notification/JpaNotificationDao.java
index 5fa156725d..3d24c6221f 100644
--- a/dao/src/main/java/org/thingsboard/server/dao/sql/notification/JpaNotificationDao.java
+++ b/dao/src/main/java/org/thingsboard/server/dao/sql/notification/JpaNotificationDao.java
@@ -81,6 +81,9 @@ public class JpaNotificationDao extends JpaAbstractDao<NotificationEntity, Notif
         return notificationRepository.updateStatusByIdAndRecipientId(notificationId.getId(), recipientId.getId(), status) != 0;
     }
 
+    /**
+     * For this hot method, the partial index `idx_notification_recipient_id_unread` was introduced since 3.5.2
+     * */
     @Override
     public int countUnreadByRecipientId(TenantId tenantId, UserId recipientId) {
         return notificationRepository.countByRecipientIdAndStatusNot(recipientId.getId(), NotificationStatus.READ);