Remove CTE ordering in shared runners query

We don't need a specific order when looking for the root ancestors

ee/app/services/ee/ci/register_job_service.rb

@@ -75,7 +75,7 @@ module EE
       # rubocop: disable CodeReuse/ActiveRecord
       def all_namespaces
         namespaces = ::Namespace.reorder(nil).where('namespaces.id = projects.namespace_id')
-        ::Gitlab::ObjectHierarchy.new(namespaces).roots
+        ::Gitlab::ObjectHierarchy.new(namespaces, options: { skip_ordering: true }).roots
       end
       # rubocop: enable CodeReuse/ActiveRecord
 

ee/changelogs/unreleased/325725-skip-ordering-for-ci-shared-runners-cte-query.yml

+---
+title: Skip ordering when using distinct in shared runners CTE query
+merge_request: 57312
+author:
+type: performance

lib/gitlab/object_hierarchy.rb

@@ -191,7 +191,7 @@ module Gitlab
     def skip_ordering?
       return options[:skip_ordering] if options.key?(:skip_ordering)
 
-      true
+      false
     end
 
     # Remove the extra `depth` field using an INNER JOIN to avoid breaking UNION queries