For ND1 in #django IRC.

celery_tasks.py

@periodic_task(crontab(...))
def taskmaster():
    acted_on = set()
    for x in MyModel.objects.filter(...).iterator():
        single_item.delay(model_id=x.pk)
        acted_on.add(x.pk)
    return acted_on
    
@task
def single_item(model_id):
    try:
        obj = MyModel.objects.filter(...).get(pk=model_id)
    except ObjectDoesNotExist:
        logger.error("oh dear", exc_info=1)
        return None
    else:
        return obj.do_something_or_other()