[wp-trac] [WordPress Trac] #48442: deleting a site leaves "orphaned" user options

[WordPress Trac]

#48442: deleting a site leaves "orphaned" user options
--------------------------------+-----------------------------
 Reporter:  pbiron              |      Owner:  (none)
     Type:  defect (bug)        |     Status:  new
 Priority:  normal              |  Milestone:  Awaiting Review
Component:  Networks and Sites  |    Version:
 Severity:  normal              |   Keywords:
  Focuses:  multisite           |
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 When a site/blog is deleted, whether from the Network > Sites screen or
 via `wp_delete_site()`, most "per site" user options (i.e., those added
 with `update_user_option()` where `$global == false`) remain in the
 `usermeta` table.  The `capabilities` and `user_level` ones are deleted,
 but all others remain.

 Core adds at least the following such user options:
 * `dashboard_quick_press_last_post_id`
 * `media_library_mode`
 * `user-settings`
 * `user-settings-time`

 and plugins often add others (e.g., classic editor adds `classic-editor-
 settings`).

 In a large network (with many users and many sites that have been deleted)
 this can result in significant bloat to the `usermeta` table.

 To reproduce:

 1. create a network and add at least 1 site in addition to the main site
 (e.g., with `blog_id == 2`)
     * can be either sub-domain or sub-directory network
 2. visit the dashboard of the site with `blog_id == 2`
         * this will create the `wp_2_dashboard_quick_press_last_post_id`
 user meta
 3. delete the site with `blog_id == 2`
 4. see that `wp_2_capabilities` and `wp_2_user_level` user metas have been
 deleted from the `usermeta` table but that
 `wp_2_dashboard_quick_press_last_post_id` remains

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Ticket URL: <https://core.trac.wordpress.org/ticket/48442>
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