Add indexes for invitations table

db/migrate/20201130132533_create_invitations.rb

@@ -8,5 +8,7 @@ class CreateInvitations < ActiveRecord::Migration[6.0]
 
       t.timestamps
     end
+    add_index :invitations, :user_id
+    add_index :invitations, :invited_user_id
   end
 end