def _rollback(self, where):

        self.output.seek(where)
        self.output.truncate()
        keys_to_delete = []
        for k, v in self.compress.iteritems():
            if v >= where:
                keys_to_delete.append(k)
        for k in keys_to_delete:
            del self.compress[k]
Truncate the output buffer at offset I{where}, and remove any
dataset/ETHPy150Open catap/namebench/nb_third_party/dns/renderer.py/Renderer._rollback