I'm running this model basically goes through each feature in a origin layer and a destination layer to calculate the shortest path. There's nothing wrong with the model, the results are perfect. However, the processing time is becoming significantly longer than the beginning - 1 second per iteration at the beginning but now it takes 6 - 7 seconds. I break the task into small parts, I tried rebooting both ArcMap and the PC, I cleaned up the system junk, I even tried disk defragment and system file check. But none of the efforts seems to accelerate the processing even a little bit. Any thoughts on how to bring the fast speed back, except for what I've tried? Or am I doing irreversible damage to my hard disk/CPU with running such a heavy task (200,000 routes)?