Originally reported a long time ago in http://bugs.musicbrainz.org/ticket/2644 and NGS seems to have a similar problem.

select count from url where ref_count = 0; gives 29489, which is too high (I count 7705 URLs with no relationships). Either the ref counts aren't being updated properly, or we're not using them at all and should just make them all zero or null or something (and later remove the column).