Basic formulation of the problem

problem.py

def do_stuff(obj):
    """Performs some simple processing on `obj`."""
    obj.y = obj.related_obj.x ** 2 + 1  # DB query to fetch `.related_obj`
    obj.save()  # DB query to update `obj`


# Obtain a large queryset for this example.
qs = MyFurstModel.objects.all()

# Simply iterate over the queryset and do some processing on each element.
# Sounds simple enough, right? WRONG!
for obj in qs:
    do_stuff(obj)