大型网站如何完成行级权限？

So I am making a small site using cakephp, and my ACL is set up so that every time a piece of content is created, an ACL rule is created to link the owner of the piece of content to the actual content. This allows each owner to edit/delete their own content. This method just seems so inefficient, because there is an equivalent amount of ACL rules as content in the database. I was curious, how do big sites, with millions of pieces of content, solve this problem?So I am making a small site using cakephp, and