Preload routes informationab-routable-nplus1

This fixes a high frequency N+1 issue:

`RoutableActions#find_routable!` is used across many controllers to
retrieve e.g. the Project or Namespace by path. The `#find_routable!`
method calls `#ensure_canonical_path` which in turn retrieves
`#full_path` from the given Routable.

This in turn triggers a lookup on `routes`, leading to a high frequency
of these queries:

```sql
SELECT  "routes".* FROM "routes" WHERE "routes"."source_id" = $1 AND
"routes"."source_type" = $2 LIMIT $3
```

This is unnecessary as we already join `routes` in
`Routable#find_by_full_path` anyways.

1 files changed, 5 insertions, 1 deletions

diff --git a/app/controllers/admin/groups_controller.rb b/app/controllers/admin/groups_controller.rb
index 6317fa7c8d1..32a36da56fe 100644
--- a/app/controllers/admin/groups_controller.rb
+++ b/app/controllers/admin/groups_controller.rb
@@ -14,7 +14,11 @@ class Admin::GroupsController < Admin::ApplicationController
 
   # rubocop: disable CodeReuse/ActiveRecord
   def show
-    @group = Group.with_statistics.joins(:route).group('routes.path').find_by_full_path(params[:id])
+    # Group.with_statistics doesn't behave nicely when including other relations.
+    # Group.find_by_full_path includes the routes relation to avoid a common N+1
+    # (at the expense of this action: there are two queries here to find and retrieve
+    # the Group with statistics).
+    @group = Group.with_statistics.find(group&.id)
     @members = present_members(
       @group.members.order("access_level DESC").page(params[:members_page]))
     @requesters = present_members(