My model's file size increases even if i do not add any 3d objects, or any process flow activities. I run the model for a long time. So the model is open for that period of time. when I close the model, and reopen it, the model becomes slow and when i look at the file size its like 4000kbs more than the size of the file when it was first opened. I save the model as a new file every time I save it.