Hierachical post types don't scale well - memory usage

[maxaud]

I recently created a custom post type that was hierarchical and was using it for data integration. I brought in 31,000 posts in the first 30 days and each post had a parent page set*. The page ran out of memory (256mb) when the post type was hierarchical. I set to false and it started to show again.

This looks to be the suspected area of holdup:
/wp-admin/includes/post.php - Line 884

 // Hierarchical types require special args.
 if ( is_post_type_hierarchical( $post_type ) && !isset($orderby) ) {
   $query['orderby'] = 'menu_order title';
   $query['order'] = 'asc';
   $query['posts_per_page'] = -1;
   $query['posts_per_archive_page'] = -1;
 }

*This is a multisite install and it may be important to note that the parent of the posts is a post of a different post_type.

[maxaud]

The page that ran out of memory was

​http://domain.com/wp-admin/edit.php?post_type=the_post_type

(When you click to view the posts in the backend.)

[duck_]

Duplicate of #15459.