'Roll back to a savepoint. Do nothing if savepoints are not supported.'

def savepoint_rollback(self, sid):

    if (not self._savepoint_allowed()):
        return
    self.validate_thread_sharing()
    self._savepoint_rollback(sid)
    self.run_on_commit = [(sids, func) for (sids, func) in self.run_on_commit if (sid not in sids)]
