The framerate in my fort has gone to hell and I can't figure out why. Not only has the activity rate gone glacial, but every minute or so the game becomes altogether unresponsive for a few seconds (like what happens when a large section of cavern collapses or you look at the stones section of the stocks screen). The recent happenings in my fort are:
* Mined out a nice, large room for tree farming, made it nice and muddy, then realized that trees wouldn't grow with all the rocks laying around and sent my dwarves in to dump them into a quantum pile. All of the activity changed the mud into sand; the gray goo has been steadily spreading throughout the fort.
* Set up an outer defensive perimeter of cage traps and hunting dogs in glass enclosures. I haven't been attacked since, even though goblins have been invading from the moment I built a trade depot.
* Dug long tunnels and fortification windows at the ends in order to map out the underground caverns without actually entering them.
* Began mass producing steel -- six dedicated magma furnaces with mid-level operators directly underneath two magnetite/coal deposits.
* Began producing soap, but promptly forbid all of it to keep my dogs from spamming job cancellations.
* Locked the hospital doors. I have a dwarf who insists on resting even though she healed long ago, plus everyone kept sleeping there and then complained about not having a room.
* There are half a dozen forgotten beasts wandering around underground and zero entry points into my fort. This has been the case for some time but didn't cause any FPS issues, unless there's something special about the last one to show up (a ravening, hairy snail with wings and a poisonous sting; right now it's chilling at the bottom of a lake).
* There are no drastic flows going on. The canal from the surface stream which I used to flood the room is floodgated shut and is slowly draining into the downstream end. The magma pool which I pumped to power my furnaces is less than 54x25 and fluctuates between depths 5 and 6 across the surface. The one flow which might be problematic is my water source / cleaning pool. It was originally going to be the power plant, but due to a long series of issues I stripped it down to a single waterwheel and pump. The system continually circulates the water to keep it clean, but the waterwheel and pump are only intermittently functional. I have no other water pipes or machines running, and my small system of magma-pipes is stagnant at depth 7.
* The population was in the 80s when the problem began, brought up to 103 by a recent immigration wave. All domestic animals except dogs and pets are kept caged.
* The adamantine veins have not been touched.
I really don't want to abandon this fort -- it's one of the best sites I've ever found, even without the new underground stuff. For once I actually have a real metal industry.
My best guess is that the tree farm is responsible. The problem seemed to start right after I drained the room and ordered the stones to be dumped, and the nasty gray sand began spreading like kudzu. If that's the case I'm hoping that I can clean it up by reflooding the room and smoothing / paving the other areas that have been infested.
What do you think?