Expose instance_get_all_uuids_by_host() from DB API and use it

We've had a long-standing optimization point in the
InstanceList.get_uuids_by_host() method, where we pull the entire
list of instance objects only to strip and return the uuids. We
already had a query method for generating just the uuids in the
DB API, but it was not exposed as it was just a helper for another
method. This exposes it publicly and uses it in that InstanceList
method.

Change-Id: I35c05e78d59ec9b95c2a443979b8d66cd42ea043

nova/db/api.py

@@ -769,6 +769,11 @@ def instance_get_all(context, columns_to_join=None):
     return IMPL.instance_get_all(context, columns_to_join=columns_to_join)
 
 
+def instance_get_all_uuids_by_host(context, host):
+    """Get a list of instance uuids on host."""
+    return IMPL.instance_get_all_uuids_by_host(context, host)
+
+
 def instance_get_all_by_filters(context, filters, sort_key='created_at',
                                 sort_dir='desc', limit=None, marker=None,
                                 columns_to_join=None):

nova/db/sqlalchemy/api.py

@@ -2607,6 +2607,11 @@ def _instance_get_all_uuids_by_host(context, host):
     return uuids
 
 
+@pick_context_manager_reader
+def instance_get_all_uuids_by_host(context, host):
+    return _instance_get_all_uuids_by_host(context, host)
+
+
 @pick_context_manager_reader
 def instance_get_all_by_host_and_node(context, host, node,
                                       columns_to_join=None):

nova/objects/instance.py

@@ -1453,11 +1453,7 @@ class InstanceList(base.ObjectListBase, base.NovaObject):
 
     @base.remotable_classmethod
     def get_uuids_by_host(cls, context, host):
-        # NOTE(danms): We could potentially do this a little more efficiently
-        # but for now just pull all the instances and scrape the uuids.
-        db_instances = db.instance_get_all_by_host(context, host,
-                                                   columns_to_join=[])
-        return [inst['uuid'] for inst in db_instances]
+        return db.instance_get_all_uuids_by_host(context, host)
 
     @staticmethod
     @db_api.pick_context_manager_reader

nova/tests/unit/db/test_db_api.py

@@ -306,6 +306,15 @@ class UnsupportedDbRegexpTestCase(DbTestCase):
                           self.context, {'display_name': '%test%'},
                           marker=uuidsentinel.uuid1)
 
+    def test_instance_get_all_uuids_by_host(self, mock_get_regexp):
+        test1 = self.create_instance_with_args(display_name='test1')
+        test2 = self.create_instance_with_args(display_name='test2')
+        test3 = self.create_instance_with_args(display_name='test3')
+        uuids = [i.uuid for i in (test1, test2, test3)]
+        found_uuids = db.instance_get_all_uuids_by_host(self.context,
+                                                        test1.host)
+        self.assertEqual(sorted(uuids), sorted(found_uuids))
+
     def _assert_equals_inst_order(self, correct_order, filters,
                                   sort_keys=None, sort_dirs=None,
                                   limit=None, marker=None,

nova/tests/unit/objects/test_instance.py

@@ -1968,19 +1968,14 @@ class _TestInstanceListObject(object):
         self.assertEqual(2, len(instances))
         self.assertEqual([1, 2], [x.id for x in instances])
 
-    @mock.patch('nova.db.instance_get_all_by_host')
+    @mock.patch('nova.db.instance_get_all_uuids_by_host')
     def test_get_uuids_by_host(self, mock_get_all):
-        fake_instances = [
-            fake_instance.fake_db_instance(id=1),
-            fake_instance.fake_db_instance(id=2),
-            ]
+        fake_instances = [uuids.inst1, uuids.inst2]
         mock_get_all.return_value = fake_instances
-        expected_uuids = [inst['uuid'] for inst in fake_instances]
         actual_uuids = objects.InstanceList.get_uuids_by_host(
             self.context, 'b')
-        self.assertEqual(expected_uuids, actual_uuids)
-        mock_get_all.assert_called_once_with(self.context, 'b',
-                                             columns_to_join=[])
+        self.assertEqual(fake_instances, actual_uuids)
+        mock_get_all.assert_called_once_with(self.context, 'b')
 
 
 class TestInstanceListObject(test_objects._LocalTest,