Adds missing index migrations by instance/status.

Adds an index for use with the migration_get_by_instance_and_status
SQL API call.

Change-Id: If2a0e8e141545aef015338b8933290c265a485d0

nova/db/sqlalchemy/migrate_repo/versions/142_add_migrations_instance_status_index.py

@@ -0,0 +1,40 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright (c) 2012 Red Hat, Inc.
+# 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
+
+
+def upgrade(migrate_engine):
+    meta = MetaData()
+    meta.bind = migrate_engine
+
+    # Based on migration_get_by_instance_and_status
+    # from: nova/db/sqlalchemy/api.py
+    t = Table('migrations', meta, autoload=True)
+    i = Index('migrations_instance_uuid_and_status_idx', t.c.deleted,
+            t.c.instance_uuid, t.c.status)
+    i.create(migrate_engine)
+
+
+def downgrade(migrate_engine):
+    meta = MetaData()
+    meta.bind = migrate_engine
+
+    t = Table('migrations', meta, autoload=True)
+    i = Index('migrations_instance_uuid_and_status_idx', t.c.deleted,
+            t.c.instance_uuid, t.c.status)
+    i.drop(migrate_engine)