Network delete user screen doesn't scale to large numbers of users

[cklosows]

Running into an issue on a MultiSite, where all users are Subscribers on the Root blog, and it's reached ~350,000 users. When trying to delete a user, the screen just ends up at this:

Missing the options to choose a new user and the delete button.

The issue is being caused by the get_users() call that is used to populate the dropdown that allows you to assign this users' post to another current user.

It may be useful to include a filter on the array parameters for this get_users call to allow people to reduce the number of users returned. In this case for us, we only ever assign the new posts to a role of 'Author' so we can pass that along as the 'role' argument with the get_users() call.

Web Server Errors show the following:

Jun 10 14:54:55 server-name lighttpd[12944]: (mod_fastcgi.c.2543) unexpected end-of-file (perhaps the fastcgi process died): pid: 12924 socket: unix:/var/run/lighttpd/php-fastcgi.socket-15
Jun 10 14:54:55 server-name lighttpd[12944]: (mod_fastcgi.c.3344) response already sent out, but backend returned error on socket: unix:/var/run/lighttpd/php-fastcgi.socket-15 for /wp-admin/network/users.php?_wpnonce=07f54ab98b&action=deleteuser&id=2340&_wp_http_referer=%2Fwp-admin%2Fnetwork%2Fusers.php%3Forderby%3Did%26order%3DDESC%26s%3Dname%2540example.com%26pc_split_value%3D4&pc_split_value=4, terminating connection

The page does fail gracefully and return a 200 response, just doesn't give the ability to complete the deletion.

[SergeyBiryukov]

#19867, #20769, #23129