模型里设置了默认作用域，如下所示：

class Article < ApplicationRecord
  ...
  default_scope   -> {order("created_at DESC")}
  ...
end

文章表设置了如下索引：

t.index ["category"], name: "index_articles_on_category"
t.index ["created_at"], name: "index_articles_on_created_at"
t.index ["user_id", "created_at"], name: "index_articles_on_user_id_and_created_at"
t.index ["user_id"], name: "index_articles_on_user_id"

为什么我使用

@articles = Article.all.paginate(page: params[:page], per_page: 10)

后按照时间排序查询不对，显示如下：

Rendering home/index.html.erb within layouts/application
   (0.3ms)  SELECT COUNT(*) FROM `articles`
Scoped order is ignored, it's forced to be batch order.
  Article Load (0.3ms)  SELECT  `articles`.* FROM `articles` ORDER BY `articles`.`id` ASC LIMIT 10 OFFSET 0
  CACHE  (0.0ms)  SELECT COUNT(*) FROM `articles`

搞不清为什么？难道是因为我用了 ruby2.5.0 和 rails 5.2.0rc1？