Cache the number of open issues and merge requests

Every project page displays a navigation menu that in turn displays the
number of open issues and merge requests. This means that for every
project page we run two COUNT(*) queries, each taking up roughly 30
milliseconds on GitLab.com. By caching these numbers and refreshing them
whenever necessary we can reduce loading times of all these pages by up
to roughly 60 milliseconds.

The number of open issues does not include confidential issues. This is
a trade-off to keep the code simple and to ensure refreshing the data
only needs 2 COUNT(*) queries instead of 3. A downside is that if a
project only has 5 confidential issues the counter will be set to 0.

Because we now have 3 similar counting service classes the code
previously used in Projects::ForksCountService has mostly been moved to
Projects::CountService, which in turn is reused by the various service
classes.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/36622

1 files changed, 5 insertions, 23 deletions

diff --git a/app/services/projects/forks_count_service.rb b/app/services/projects/forks_count_service.rb
index e2e2b1da91d..3a0fa84b868 100644
--- a/app/services/projects/forks_count_service.rb
+++ b/app/services/projects/forks_count_service.rb
@@ -1,30 +1,12 @@
 module Projects
   # Service class for getting and caching the number of forks of a project.
-  class ForksCountService
-    def initialize(project)
-      @project = project
+  class ForksCountService < CountService
+    def relation_for_count
+      @project.forks
     end
 
-    def count
-      Rails.cache.fetch(cache_key) { uncached_count }
-    end
-
-    def refresh_cache
-      Rails.cache.write(cache_key, uncached_count)
-    end
-
-    def delete_cache
-      Rails.cache.delete(cache_key)
-    end
-
-    private
-
-    def uncached_count
-      @project.forks.count
-    end
-
-    def cache_key
-      ['projects', @project.id, 'forks_count']
+    def cache_key_name
+      'forks_count'
     end
   end
 end