Here's what I was observing on several worlds:
Click on mini-map, watch character run/halt/run/halt/run/halt. Watch NPC's move/halt/move/halt/move/halt.
Two words spring to mind: RESOURCE STARVATION.
I know virtualization of servers is all the rage these days, but if you've over-virtualized (putting too many virtual machines on a physical server), you'll experience terrible performance (lack of CPU clock ticks, memory, network bandwidth, etc...)
The obvious answer would have been to call up the application server provider (assuming that you lease your physical hardware servers rather than own your own), and have them add additional physical servers, then re-distribute some of the virtual servers from the overloaded physical machines to the new one(s). (Better load balancing.) It's the same idea if you own, or course, though that would require you have servers "at the ready" to throw at the problem, and that's not likely on a weekend.
I managed to find a world that wasn't too bad, but you could still observe degraded performance.
30-Oct-2012 18:19:27