Merge "Avoid unnecessary joins in InstanceGroup.get_hosts" into stable/stein

Author: Zuul

nova/objects/instance_group.py

@@ -497,8 +497,15 @@ def get_hosts(self, exclude=None):
         if exclude:
             filter_uuids = set(filter_uuids) - set(exclude)
         filters = {'uuid': filter_uuids, 'deleted': False}
+        # Pass expected_attrs=[] to avoid unnecessary joins.
+        # TODO(mriedem): This is pretty inefficient since all we care about
+        # are the hosts. We could optimize this with a single-purpose SQL query
+        # like:
+        #   SELECT host FROM instances WHERE deleted=0 AND host IS NOT NULL
+        #       AND uuid IN ($filter_uuids) GROUP BY host;
         instances = objects.InstanceList.get_by_filters(self._context,
-                                                        filters=filters)
+                                                        filters=filters,
+                                                        expected_attrs=[])
         return list(set([instance.host for instance in instances
                          if instance.host]))
 

nova/tests/unit/objects/test_instance_group.py

@@ -280,7 +280,8 @@ def test_get_hosts(self, mock_get_db, mock_il_get):
             'deleted': False
         }
         mock_il_get.assert_called_once_with(self.context,
-                                            filters=expected_filters)
+                                            filters=expected_filters,
+                                            expected_attrs=[])
         self.assertEqual(2, len(hosts))
         self.assertIn('host1', hosts)
         self.assertIn('host2', hosts)
@@ -293,7 +294,8 @@ def test_get_hosts(self, mock_get_db, mock_il_get):
             'deleted': False
         }
         mock_il_get.assert_called_once_with(self.context,
-                                            filters=expected_filters)
+                                            filters=expected_filters,
+                                            expected_attrs=[])
 
     def test_obj_make_compatible(self):
         obj = objects.InstanceGroup(self.context, **_INST_GROUP_OBJ_VALS)