'Make a key that is used for counter values.'

def make_counter_key(self, model, epoch, model_key):

    if isinstance(model_key, six.integer_types):
        vnode = (model_key % self.vnodes)
    else:
        if isinstance(model_key, six.text_type):
            model_key = model_key.encode('utf-8')
        vnode = (crc32(model_key) % self.vnodes)
    return '{0}{1}:{2}:{3}'.format(self.prefix, model.value, epoch, vnode)
