Prevent mirror service from calling Gitaly too much

app/services/projects/update_remote_mirror_service.rb

@@ -128,7 +128,7 @@ module Projects
 
         remote_ref_id = remote_ref.dereferenced_target.try(:id)
 
-        if remote_ref_id && project.repository.is_ancestor?(remote_ref_id, default_branch_id)
+        if remote_ref_id && project.repository.rugged_is_ancestor?(remote_ref_id, default_branch_id)
           refs_to_delete << name
         end
       end

lib/gitlab/git/repository.rb

@@ -360,6 +360,13 @@ module Gitlab
         rugged.merge_base(from, to)
       end
 
+      # Gitaly note: JV: check gitlab-ee before removing this method.
+      def rugged_is_ancestor?(ancestor_id, descendant_id)
+        return false if ancestor_id.nil? || descendant_id.nil?
+
+        merge_base_commit(ancestor_id, descendant_id) == ancestor_id
+      end
+
       # Returns true is +from+ is direct ancestor to +to+, otherwise false
       def is_ancestor?(from, to)
         gitaly_commit_client.is_ancestor(from, to)