I'm pretty sure this uses the map reduce API which has a lot of overhead in the datastore. In principle map reduce is nice because it could make very large jobs fast. But since Google engineers don't pay for anything, they optimized for time, not cost.
And with regards to your script, you can't just delete 3k keys in one request. If you want I'll send you the script I've adapted for jobs that make large changes to the datastore.
And with regards to your script, you can't just delete 3k keys in one request. If you want I'll send you the script I've adapted for jobs that make large changes to the datastore.