new_contents: # Copyright 2013 Rackspace Hosting
  # All Rights Reserved.
  #
  #    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 sqlalchemy import Index, MetaData, Table
  
  
  TABLE_NAME = 'compute_node_stats'
  IDX_NAME = 'compute_node_stats_node_id_and_deleted_idx'
  
  
  def upgrade(migrate_engine):
      """Add an index to make the scheduler lookups of compute_nodes and joined
      compute_node_stats more efficient.
      """
      meta = MetaData(bind=migrate_engine)
      cn_stats = Table(TABLE_NAME, meta, autoload=True)
      idx = Index(IDX_NAME, cn_stats.c.compute_node_id, cn_stats.c.deleted)
      idx.create(migrate_engine)
  
  
  def downgrade(migrate_engine):
      meta = MetaData(bind=migrate_engine)
      cn_stats = Table(TABLE_NAME, meta, autoload=True)
      idx = Index(IDX_NAME, cn_stats.c.compute_node_id, cn_stats.c.deleted)
      idx.drop(migrate_engine)
  
subject: Add an index to compute_node_stats