Author here - I'm afraid it is hugely wasteful. The network is really nothing to do with it but instead the fact that you have to make a table read instead of an index read. This seems like a small thing but as I describe it changes the complexity class of the algorithm you have effectively written.
How does it change the complexity class of an algorithm?
Database performing a table read because additional columns were requested shouldn't change the complexity class if the query was otherwise successfully satisfied using the index.
I searched the article for "complexity class" and, while I found the phrase, it didn't explain much.
Sorry, yes, you're right. It doesn't change the complexity class just because you have to go to the heap. It is however a lot slower for the usual reasons: the heap is less dense in memory, it's a second thing you have to do, you have to serialise/deserialise more, etc etc.
But yes, you're right: just going to the heap is not a change in complexity class.
