AFAIK the simplest way to delete them which requires *no code to be written* is the deprecated but still working datastore admin. In your Google Cloud Console go to Datastore > Admin click on "Open Datastore Admin", select the entity kind you want to delete and click "Delete Entities". This will kick off a distributed, fan-out map reduce job which will delete the entities in a couple of hours.
Of course, as Vitaly said, this will cost you money. Attila -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to google-appengine+unsubscr...@googlegroups.com. To post to this group, send email to google-appengine@googlegroups.com. Visit this group at https://groups.google.com/group/google-appengine. To view this discussion on the web visit https://groups.google.com/d/msgid/google-appengine/2b0c0945-16ee-48d0-8a4b-bf256a8b6ef0%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
