Merge "Optimize populate_queued_for_delete online data migration"

nova/objects/instance_mapping.py

@@ -161,12 +161,14 @@ def populate_queued_for_delete(context, max_count):
             # have not yet received a defined value decision for
             # queued_for_delete
             context.session.query(api_models.InstanceMapping)
-            .options(joinedload('cell_mapping'))
             .filter(
                 api_models.InstanceMapping.queued_for_delete == None)  # noqa
             .filter(api_models.InstanceMapping.cell_id == cell.id)
             .limit(max_count).all())
         ims_by_inst = {im.instance_uuid: im for im in ims}
+        if not ims_by_inst:
+            # If there is nothing from this cell to migrate, move on.
+            continue
         with nova_context.target_cell(context, cell) as cctxt:
             filters = {'uuid': list(ims_by_inst.keys()),
                        'deleted': True,

nova/tests/functional/db/test_instance_mapping.py

@@ -10,6 +10,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import mock
 from oslo_utils.fixture import uuidsentinel
 from oslo_utils import uuidutils
 
@@ -196,6 +197,15 @@ class InstanceMappingTestCase(test.NoDBTestCase):
         self.assertEqual(4, len(
             [im for im in mappings if im.queued_for_delete is False]))
 
+        # Run it again to make sure we don't query the cell database for
+        # instances if we didn't get any un-migrated mappings.
+        with mock.patch('nova.objects.InstanceList.get_by_filters',
+                        new_callable=mock.NonCallableMock):
+            done, total = instance_mapping.populate_queued_for_delete(
+                self.context, 1000)
+        self.assertEqual(0, done)
+        self.assertEqual(0, total)
+
 
 class InstanceMappingListTestCase(test.NoDBTestCase):
     USES_DB_SELF = True