original thread (search for Salamander)

This is a bandwagon that just won’t roll very far, and the reason – as usual – is obvious to people who’ve studied the field for a while. Naively implemented, a P2P protocol tends to generate O(n^2) messages for a given workload, where N is the number of nodes. This can often be brought down to O(n) but only with absolutely top-notch developers and a lot of effort. Better than O(n) is usually impossible.

By contrast, hierarchical systems tend to hover between O(n) and O(log(n)) depending on the particular problem. This does not necessarily apply only to single-rooted hierarchies, either. A multi-rooted hierarchy tends to exhibit the same scaling behavior, though of course the more roots you have the more you start to look like P2P and share its scaling characteristics.

The long and the short of it is that P2P just doesn’t scale well. Even the best-implemented P2P protocol can merely approach the message efficiency of a naively implemented hierarchical protocol. For large numbers of nodes this results in the P2P implementation simply getting swamped. The only question is how large and how swamped it has to be before it becomes unusable.