Oh no if you want every name, then you want a full table scan - I just mean in a real application using the database, I highly suggest not building against using has(). Like, you want all the names of Persons, so you would do names(func: type(Person)){name} - which would use the index on dgraph.type to get only uids that have dgraph.type=“Person”, then go to the name tablet, and pull values for each of those uids. Just meant as a suggestion as you build out an application, not to be applied to the test IMDB dataset per se.
I do not understand a reason behind your observation about asking for 603 is fastish but 604 is slow, so I wont comment on that. (by the way I have reproduced that myself on there)