Add an index on aggregate_metadata.value

We need this for the subsequent request_filter, which will do queries
based only on metadata value.

Related to blueprint placement-req-filter

Change-Id: I1325a226823329384edd7197e5d5f2725dc16e8f

nova/db/sqlalchemy/migrate_repo/versions/389_add_aggregate_metadata_index.py

@@ -0,0 +1,44 @@
+#    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_log import log as logging
+from sqlalchemy import MetaData, Table, Index
+
+LOG = logging.getLogger(__name__)
+
+INDEX_COLUMNS = ['value']
+INDEX_NAME = 'aggregate_metadata_value_idx'
+TABLE_NAME = 'aggregate_metadata'
+
+
+def _get_table_index(migrate_engine):
+    meta = MetaData()
+    meta.bind = migrate_engine
+    table = Table(TABLE_NAME, meta, autoload=True)
+    for idx in table.indexes:
+        if idx.columns.keys() == INDEX_COLUMNS:
+            break
+    else:
+        idx = None
+    return table, idx
+
+
+def upgrade(migrate_engine):
+    table, index = _get_table_index(migrate_engine)
+    if index:
+        LOG.info('Skipped adding %s because an equivalent index'
+                 ' already exists.', INDEX_NAME)
+        return
+    columns = [getattr(table.c, col_name) for col_name in INDEX_COLUMNS]
+    index = Index(INDEX_NAME, *columns)
+    index.create(migrate_engine)

nova/db/sqlalchemy/models.py

@@ -1132,6 +1132,7 @@ class AggregateMetadata(BASE, NovaBase, models.SoftDeleteMixin):
             name="uniq_aggregate_metadata0aggregate_id0key0deleted"
             ),
         Index('aggregate_metadata_key_idx', 'key'),
+        Index('aggregate_metadata_value_idx', 'value'),
     )
     id = Column(Integer, primary_key=True)
     key = Column(String(255), nullable=False)

nova/tests/unit/db/test_migrations.py

@@ -999,6 +999,11 @@ class NovaMigrationsCheckers(test_migrations.ModelsMigrationsSync,
             'instance_actions_instance_uuid_updated_at_idx',
             ['instance_uuid', 'updated_at'])
 
+    def _check_389(self, engine, data):
+        self.assertIndexMembers(engine, 'aggregate_metadata',
+                                'aggregate_metadata_value_idx',
+                                ['value'])
+
 
 class TestNovaMigrationsSQLite(NovaMigrationsCheckers,
                                test_base.DbTestCase,