Explain query counts

Fix trivial excesses (2 splits configured & don't fetch courses if there are none)
LMS-11220, LMS-11391, LMS-11390

cms/djangoapps/contentstore/tests/test_course_listing.py

@@ -200,12 +200,14 @@ class TestCourseListing(ModuleStoreTestCase):
         self.assertGreaterEqual(iteration_over_courses_time_2.elapsed, iteration_over_groups_time_2.elapsed)
 
         # Now count the db queries
-        store = modulestore()._get_modulestore_by_type(ModuleStoreEnum.Type.mongo)
         with check_mongo_calls(USER_COURSES_COUNT):
             _accessible_courses_list_from_groups(self.request)
 
-        # TODO: LMS-11220: Document why this takes 6 calls
-        with check_mongo_calls(6):
+        # Calls:
+        #    1) query old mongo
+        #    2) get_more on old mongo
+        #    3) query split (but no courses so no fetching of data)
+        with check_mongo_calls(3):
             _accessible_courses_list(self.request)
 
     def test_get_course_list_with_same_course_id(self):
@@ -276,7 +278,7 @@ class TestCourseListing(ModuleStoreTestCase):
         course_location = SlashSeparatedCourseKey('testOrg', 'erroredCourse', 'RunBabyRun')
         course = self._create_course_with_access_groups(course_location, self.user)
         course_db_record = store._find_one(course.location)
-        course_db_record.setdefault('metadata', {}).get('tabs', []).append({"type": "wiko", "name": "Wiki" })
+        course_db_record.setdefault('metadata', {}).get('tabs', []).append({"type": "wiko", "name": "Wiki"})
         store.collection.update(
             {'_id': course.location.to_deprecated_son()},
             {'$set': {

cms/envs/test.py

@@ -73,17 +73,6 @@ STATICFILES_STORAGE='pipeline.storage.NonPackagingPipelineStorage'
 STATIC_URL = "/static/"
 PIPELINE_ENABLED=False
 
-# Add split as another store for testing
-MODULESTORE['default']['OPTIONS']['stores'].append(
-    {
-        'NAME': 'split',
-        'ENGINE': 'xmodule.modulestore.split_mongo.split_draft.DraftVersioningModuleStore',
-        'DOC_STORE_CONFIG': DOC_STORE_CONFIG,
-        'OPTIONS': {
-            'render_template': 'edxmako.shortcuts.render_to_string',
-        }
-    },
-)
 # Update module store settings per defaults for tests
 update_module_store_settings(
     MODULESTORE,

common/lib/xmodule/xmodule/modulestore/split_mongo/split.py

@@ -681,6 +681,9 @@ class SplitMongoModuleStore(SplitBulkWriteMixin, ModuleStoreWriteBase):
             version_guids.append(version_guid)
             id_version_map[version_guid] = course_index
 
+        if not version_guids:
+            return []
+
         matching_structures = self.find_structures_by_id(version_guids)
 
         # get the blocks for each course index (s/b the root)

common/lib/xmodule/xmodule/modulestore/tests/test_publish.py

@@ -89,11 +89,21 @@ class TestPublish(SplitWMongoCourseBoostrapper):
         """
         vert_location = self.old_course_key.make_usage_key('vertical', block_id='Vert1')
         item = self.draft_mongo.get_item(vert_location, 2)
-        # Vert1 has 3 children; so, publishes 4 nodes which may mean 4 inserts & 1 bulk remove
-        # TODO: LMS-11220: Document why find count is 25
-        # 25-June-2014 find calls are 19. Probably due to inheritance recomputation?
-        # 02-July-2014 send calls are 7. 5 from above, plus 2 for updating subtree edit info for Chapter1 and course
-        #              find calls are 22. 19 from above, plus 3 for finding the parent of Vert1, Chapter1, and course
+        # Finds:
+        #   1 get draft vert,
+        #   2-10 for each child: (3 children x 3 queries each)
+        #      get draft and then published child
+        #      compute inheritance
+        #   11 get published vert
+        #   12-15 get each ancestor (count then get): (2 x 2),
+        #   16 then fail count of course parent (1)
+        #   17 compute inheritance
+        #   18 get last error
+        #   19-20 get draft and published vert
+        # Sends:
+        #   delete the subtree of drafts (1 call),
+        #   update the published version of each node in subtree (4 calls),
+        #   update the ancestors up to course (2 calls)
         with check_mongo_calls(20, 7):
             self.draft_mongo.publish(item.location, self.user_id)