Reduce DB calls when getting an image

Right now if you want to get a single image, two queries need to be
executed:
- Get image + associated locations and properties
- Get associated tags for image

Proposed solution combines these two queries into single one which gets
image and all related data - locations, properties and tags. Similar
pattern has been already implemented when querying for list of images.

Change-Id: Ic4424bb1eb1769d8f621ebe111d95961ecf08479
Closes-Bug: 1434578

glance/db/__init__.py

@@ -66,13 +66,14 @@ class ImageRepo(object):
 
     def get(self, image_id):
         try:
-            db_api_image = dict(self.db_api.image_get(self.context, image_id))
+            db_api_image = dict(self.db_api.image_get(self.context,
+                                                      image_id,
+                                                      return_tag=True))
             assert not db_api_image['deleted']
         except (exception.NotFound, exception.Forbidden, AssertionError):
             msg = _("No image found with ID %s") % image_id
             raise exception.NotFound(msg)
-        tags = self.db_api.image_tag_get_all(self.context, image_id)
-        image = self._format_image_from_db(db_api_image, tags)
+        image = self._format_image_from_db(db_api_image, db_api_image['tags'])
         return ImageProxy(image, self.context, self.db_api)
 
     def list(self, marker=None, limit=None, sort_key=None,

glance/db/registry/api.py

@@ -83,9 +83,10 @@ def image_destroy(client, image_id):
 
 
 @_get_client
-def image_get(client, image_id, force_show_deleted=False):
+def image_get(client, image_id, force_show_deleted=False, return_tag=False):
     return client.image_get(image_id=image_id,
-                            force_show_deleted=force_show_deleted)
+                            force_show_deleted=force_show_deleted,
+                            return_tag=return_tag)
 
 
 def is_image_visible(context, image, status=None):

glance/db/simple/api.py

@@ -380,7 +380,8 @@ def _sort_images(images, sort_key, sort_dir):
     return images
 
 
-def _image_get(context, image_id, force_show_deleted=False, status=None):
+def _image_get(context, image_id, force_show_deleted=False, status=None,
+               return_tag=False):
     try:
         image = DATA['images'][image_id]
     except KeyError:
@@ -396,12 +397,18 @@ def _image_get(context, image_id, force_show_deleted=False, status=None):
         LOG.warn(_LW('Unable to get unowned image'))
         raise exception.Forbidden("Image not visible to you")
 
+    if return_tag:
+        image['tags'] = image_tag_get_all(context, image_id)
+
     return image
 
 
 @log_call
-def image_get(context, image_id, session=None, force_show_deleted=False):
-    image = _image_get(context, image_id, force_show_deleted)
+def image_get(context, image_id, session=None, force_show_deleted=False,
+              return_tag=False):
+    image = _image_get(context, image_id, force_show_deleted,
+                       return_tag=return_tag)
+
     return _normalize_locations(context, copy.deepcopy(image),
                                 force_show_deleted=force_show_deleted)
 

glance/db/sqlalchemy/api.py

@@ -196,11 +196,17 @@ def _normalize_tags(image):
     return image
 
 
-def image_get(context, image_id, session=None, force_show_deleted=False):
+def image_get(context, image_id, session=None, force_show_deleted=False,
+              return_tag=False):
     image = _image_get(context, image_id, session=session,
-                       force_show_deleted=force_show_deleted)
+                       force_show_deleted=force_show_deleted,
+                       return_tag=return_tag)
     image = _normalize_locations(context, image.to_dict(),
                                  force_show_deleted=force_show_deleted)
+
+    if return_tag:
+        image = _normalize_tags(image)
+
     return image
 
 
@@ -218,7 +224,8 @@ def _check_image_id(image_id):
         raise exception.NotFound()
 
 
-def _image_get(context, image_id, session=None, force_show_deleted=False):
+def _image_get(context, image_id, session=None, force_show_deleted=False,
+               return_tag=False):
     """Get an image or raise if it does not exist."""
     _check_image_id(image_id)
     session = session or get_session()
@@ -233,6 +240,9 @@ def _image_get(context, image_id, session=None, force_show_deleted=False):
         if not force_show_deleted and not context.can_see_deleted:
             query = query.filter_by(deleted=False)
 
+        if return_tag:
+            query = query.options(sa_orm.joinedload(models.Image.tags))
+
         image = query.one()
 
     except sa_orm.exc.NoResultFound:

glance/tests/functional/db/base.py

@@ -382,6 +382,28 @@ class DriverTests(object):
                                       force_show_deleted=True)
         self.assertEqual(self.fixtures[0]['id'], image['id'])
 
+    def test_image_get_with_tag_returning(self):
+        expected_tags = {UUID1: ['foo'], UUID2: ['bar'], UUID3: ['baz']}
+
+        self.db_api.image_tag_create(self.context, UUID1,
+                                     expected_tags[UUID1][0])
+        self.db_api.image_tag_create(self.context, UUID2,
+                                     expected_tags[UUID2][0])
+        self.db_api.image_tag_create(self.context, UUID3,
+                                     expected_tags[UUID3][0])
+
+        image = self.db_api.image_get(self.context, UUID1, return_tag=True)
+        self.assertEqual(self.fixtures[0]['id'], image['id'])
+        self.assertEqual(expected_tags[image['id']], image['tags'])
+
+        self.db_api.image_tag_delete(self.context, UUID1,
+                                     expected_tags[UUID1][0])
+        expected_tags[UUID1] = []
+
+        image = self.db_api.image_get(self.context, UUID1, return_tag=True)
+        self.assertEqual(self.fixtures[0]['id'], image['id'])
+        self.assertEqual(expected_tags[image['id']], image['tags'])
+
     def test_image_get_not_owned(self):
         TENANT1 = str(uuid.uuid4())
         TENANT2 = str(uuid.uuid4())