Here's a snippet of information I learned from James Stallings, who is the support person behind the hosting company for four Devokan islands and also an OSgrid admin. I checked beforehand that it was OK to post this information.
I asked why sometimes avies are unable to move (walking or flying) in some islands but not others when they are all on the same server.
I went on to ask: 'In a mega-region, is there only one instance of OCE Physics? Is that one reason (I suspect there may be others) why the internal boundary transitions are so much smoother?'James wrote:ODE Physics. Each region has its own instance.
ODE is a serious pain because 1. it's a very good physics engine (simulates quite well). 2. It was designed for science simulations, not gaming, so has a lot of weird quirks - where we'd like it to ignore a particularly troublesome set of physics problems altogether (DeepThink), and keep happily simulating, most of science wants it to stop simulating at once and report on the circumstances of the physics problem so, much of 'debugging' ODE has had to do with changing that basic philosophy.
OpenSim itself is -very- stable; witness the fact that even with the physics engine crashed, one can still carry on chatting, building, and sitting your way around the region.
James wrote:yes that is one reason the boundaries pretty much dissolve in a mega - also, in mega, if physics dies, it dies for the whole mega