In last night's ModBot run, it spent 7 minutes on empty artists, 1 minute on empty labels, 25 minutes on empty release groups and 15 minutes on empty works. The artist and label queries don't join the edit table because edit_artist and edit_label have a status column. The release group and label do join the edit table because edit_release_group and edit_label don't have a status column.

https://github.com/metabrainz/musicbrainz-server/blob/master/admin/sql/CreateFunctions.sql