Deprecation: improve Celery task db query

This commit excludes the users that already have an unread notification with
this message. This is only to avoid performing db queries for users where our
notification backend won't add a new notification anyways. This will improve the
performance of this task making it to run faster (hopefully).

Author: humitos

readthedocs/projects/tasks/utils.py

@@ -271,6 +271,14 @@ def deprecated_config_file_used_notification():
     queryset = User.objects.filter(username__in=users, profile__banned=False).order_by(
         "id"
     )
+
+    # Exclude users that already have an unread notification.
+    # Our notifications backend already performs de-duplication of notifications automatically.
+    # However, this is only to speed up things here since this loop takes the most time.
+    queryset = queryset.exclude(
+        message__message__startswith="Your project(s)", message__read=False
+    )
+
     n_users = queryset.count()
     for i, user in enumerate(queryset.iterator()):
         if i % 500 == 0: