This answer is pretty much obsolete, since i don’t think anyone really uses territories much anymore, but…
The most brokers i have ever seen in a territory is seven. There are problems with territories that create performance issues, particularly with guaranteed information that must be propagated to all subscribing brokers within a territory. One client i had – the same one with seven brokers in a territory, had all seven brokers on the same broker server. This was a major problem, since broker servers have one guaranteed storage system (and swap file). By having all the brokers on the same broker server in the same territory, the effective space in the guaranteed storage system was reduced by a factor of seven (More generally, 1/the number of brokers). They routinely overran their swap space, crashing the brokers, and corrupting the guaranteed storage file. There was also some isolated problems where a subscription on one broker in this territory would become “ignored” and the only solution we found was to rebuild the broker from the ground up.
To answer your other question, i saw a client with about forty brokers on about six machines.
No distance limit (as long as we are confined to the Earth).
Territories and multiple brokers can become very complicated, both to coordinate, install, and maintain. Many clients use a monolithic broker to keep things simple, and most of the time, i agree with them that one large broker box (plus optional clustering) with one broker, is the right solution.
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