old_contents: # -*- coding: utf-8 -*-
  
  # Copyright 2010-2011 OpenStack Foundation
  # Copyright (c) 2013 Hewlett-Packard Development Company, L.P.
  #
  # Licensed under the Apache License, Version 2.0 (the "License"); you may
  # not use this file except in compliance with the License. You may obtain
  # a copy of the License at
  #
  #      http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  # License for the specific language governing permissions and limitations
  # under the License.
  
  
  from oslo.config import cfg
  from stevedore import driver
  
  from volt.openstack.common.gettextutils import _
  
  EXECUTOR_NAMESPACE = 'volt.executor'
  
  executor_opts = [
      cfg.StrOpt('default_executor', default='btree',
                 help=_('The default volume tracker algorithm executor.')
      ),
  ]
  
  CONF = cfg.CONF
  CONF.register_opts(executor_opts)
  
  EXECUTOR = None
  
  
  def get_default_executor():
      global EXECUTOR
  
      if EXECUTOR is None:
          EXECUTOR = driver.DriverManager(
              EXECUTOR_NAMESPACE, CONF.default_executor,
              invoke_on_load=True
          )
      return EXECUTOR.driver
  
  
  class Executor(object):
      """ The Base class of Executor
      """
      def __init__(self):
          pass
  
      def get_volumes_list(self):
          raise NotImplementedError()
  
      def get_volumes_detail(self, volume_id):
          raise NotImplementedError()
  
      def add_volume_metadata(self, volume_id, peer_id, **kwargs):
          raise NotImplementedError()
  
      def delete_volume_metadata(self, volume_id,  peer_id):
          raise NotImplementedError()
  
      def get_volume_parents(self, volume_id, peer_id=None, host=None):
          raise NotImplementedError()
  
      def update_status(self, host):
          raise NotImplementedError()
  
new_contents: # -*- coding: utf-8 -*-
  
  # Copyright 2010-2011 OpenStack Foundation
  # Copyright (c) 2013 Hewlett-Packard Development Company, L.P.
  #
  # Licensed under the Apache License, Version 2.0 (the "License"); you may
  # not use this file except in compliance with the License. You may obtain
  # a copy of the License at
  #
  #      http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  # License for the specific language governing permissions and limitations
  # under the License.
  
  
  from oslo.config import cfg
  from stevedore import driver
  
  from volt.openstack.common.gettextutils import _
  
  EXECUTOR_NAMESPACE = 'volt.executor'
  
  executor_opts = [
      cfg.StrOpt('default_executor', default='btreewithuncle',
                 help=_('The default volume tracker algorithm executor.')
      ),
  ]
  
  CONF = cfg.CONF
  CONF.register_opts(executor_opts)
  
  EXECUTOR = None
  
  
  def get_default_executor():
      global EXECUTOR
  
      if EXECUTOR is None:
          EXECUTOR = driver.DriverManager(
              EXECUTOR_NAMESPACE, CONF.default_executor,
              invoke_on_load=True
          )
      return EXECUTOR.driver
  
  
  class Executor(object):
      """ The Base class of Executor
      """
      def __init__(self):
          pass
  
      def get_volumes_list(self):
          raise NotImplementedError()
  
      def get_volumes_detail(self, volume_id):
          raise NotImplementedError()
  
      def add_volume_metadata(self, volume_id, peer_id, **kwargs):
          raise NotImplementedError()
  
      def delete_volume_metadata(self, volume_id,  peer_id):
          raise NotImplementedError()
  
      def get_volume_parents(self, volume_id, peer_id=None, host=None):
          raise NotImplementedError()
  
      def update_status(self, host):
          raise NotImplementedError()
  
subject: Change the default executor to btreewithuncle.