Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1080 with Max-Q Design/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.48
Broken: version: 2.82 (sub 0), branch: master, commit date: 2019-10-14 16:48, hash: rB519891c6695f
Short description of error
The separate by loose parts tool hangs on large meshes.
Yes it's a fairly large mesh, but tools like select linked or even separate by selection do not have much problem with it. However separate by loose parts takes (forever?) I had to close Blender after 3 hours.
Exact steps for others to reproduce the error
Enter edit mode
Separate by Loose Parts
blender Separate.blend -b --python-expr "import bpy, time; bpy.ops.object.editmode_toggle(); t = time.time(); print('Objects:', len(bpy.data.objects)); bpy.ops.mesh.separate(type='LOOSE'); print('Seconds:', time.time() - t, 'Objects:', len(bpy.data.objects))"