Wrapped local_comments also in a cache

closes #8241
closes #7992

Changelog.md

@@ -1,6 +1,7 @@
 # 0.7.16.0
 
 ## Refactor
+* Cache local posts/comments count for statistics [#8241](https://github.com/diaspora/diaspora/pull/8241)
 
 ## Bug fixes
 

app/presenters/node_info_presenter.rb

@@ -114,8 +114,10 @@ class NodeInfoPresenter
   end
 
   def local_comments
-    @local_comments ||= Comment.joins(:author)
-                               .where.not(people: {owner_id: nil})
-                               .count
+    Rails.cache.fetch("NodeInfoPresenter/local_comments", expires_in: 1.hour) do
+      @local_comments ||= Comment.joins(:author)
+                                 .where.not(people: {owner_id: nil})
+                                 .count
+    end
   end
 end