I'm guessing something that added some categories to some very widely used infobox or licensing templates.
external links for each language in license templates for now I made that all 'external links' pointing to self are not saved in links tables, which makes an easy workaround for most obvious cases...
every object in the database ended up having hundreds of various links entries, some of which, like ones in externallinks, are quite big (avg is around 250 bytes per row, thats without indexing costs).
Domas