[Anderkent]

Their initial test case was a full clone, in which case you can't really send a shallow pack.

The problem, as I understand it, was that when you requested a full clone of fork1/repo.git, they'd find all objects reachable from refs in that repo, but git would by default generate deltas for those objects that referred to objects from other forks. When it noticed those objects were not going to be sent to the client, nor did client know about them, git recovered by doing expensive matching across the objects that it was sending, and without having traversed the graph before its heuristics weren't working properly so this took forever.