code: public void rollback()
          throws DBException, RemoteException
      {
          BaseTransport transport = this.createProxyTransport(ROLLBACK);
          Object strReturn = transport.sendMessageAndGetReply();
          Object objReturn = transport.convertReturnObject(strReturn);
          this.checkDBException(objReturn);
      }
docs: Rollback the transactions since the last commit.
  Override this for SQL implementations.
  @exception DBException An exception.