Reduce user_meta bloat for super admin users

[ryan]

Super admins have {$blog_id}_user-settings, {$blog_id}_user-settings-time, and {$blog_id}_dashboard_quick_press_last_post_id usermeta entries added for every dashboard they visit, regardless of whether they are a user on the blog or not. The end result is that some super admins have many thousands of usermeta entries and a user object possibly over 1MB. We have seen several in the 800k range containing these entries for over 300 blogs.

[nacin]

I wonder if we can just toss out dashboard_quick_press_last_post_id by always just generating an auto-draft on the fly for QuickPress. Avoiding a single insert query doesn't seem like the end of the world, and cron cleans them up.

Or, should QuickPress be hidden for users that, minus their super admin capabilities, don't actually have posting access?

I think it is fine to avoid saving user settings in the DB when super admins wouldn't otherwise have access to the dashboard. Let it stay in the cookie and that's it.

[nacin]

Things currently handled by user settings: folding/unfolding of the admin menu, which editor you use by default (tinymce v html), your editor height, your DFW width, your default gallery settings (columns, etc.), plupload versus html4 uploader, default image properties (alignment, size, where it links to), internal linking expansion. So, decent amount of stuff, but nothing that is much of an issue.

Kind of weird that folding/unfolding of the admin menu isn't global, though.

[ryan]

That could be refined to go ahead and update the options if they are already present.

[ryan]

Handle dashboard_quick_press_last_post_id

[ryan]

Clean up

[ryan]

In [22256]:

Don't create {$blog_id}_user-settings, {$blog_id}_user-settings-time, and {$blog_id}_dashboard_quick_press_last_post_id user options when a super admin visits a site they aren't a member of. Instead, rely solely on the wp-settings cookie.

fixes #22178