[wp-trac] [WordPress Trac] #32474: Facilitate widgets to be stored in posts instead of options

[WordPress Trac]

#32474: Facilitate widgets to be stored in posts instead of options
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 Reporter:  westonruter  |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  normal       |  Milestone:  4.3
Component:  Widgets      |    Version:  2.8
 Severity:  normal       |   Keywords:  has-patch
  Focuses:               |
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 Widget instance data has always been stored in `wp_options`. This worked
 fine when there were only a few widgets used on a site. When there are
 hundreds—or thousands—there are big performance problems. When
 initializing widgets, Core loads the entire settings arrays of all widgets
 even when they are not used (#23909). Additionally, widget settings
 options are by default autoloaded: this means that for widget-heavy sites
 using Memcached Object Cache will reach the 1MB limit and crash since the
 autoloaded options will no longer be cacheable (WordPress.com even
 [https://github.com/Automattic/vip-quickstart/blob/master/www/wp-content
 /mu-plugins/alloptions-limit.php block a site from loading] in this
 scenario). Storage in autoloaded options also means widgets are
 susceptible to alloptions cache corruption (#31245). Bottom line: widgets
 stored in options are not scalable.

 As I've [https://core.trac.wordpress.org/ticket/31436#comment:2 mentioned
 elsewhere], widgets should ideally be stored in posts instead of options.
 In addition to improving the performance problems above, there are many
 advantaged to storing widgets as posts, including user attribution via
 `post_author`, revision history, import/export, querying, widget drafts,
 scheduled widgets,  etc.

 Changing the storage mechanism for widgets is a major change, but with a
 couple small changes to `WP_Widget`, Core can easily support alternative
 widget instance storage systems, all through the
 `pre_option_widget_{$id_base}` and `pre_update_option_{$id_base}` filters.

 The `WP_Widget` change is to allow settings to be array-like objects,
 specifically `ArrayIterator`. A plugin then can implement the
 `offsetGet()` and `current()` methods for an `ArrayIterator` subclass to
 lazy-load data from posts only when it is needed. Otherwise, the only data
 needed for WordPress at `widgets_init` are shallow arrays of multi-widget
 numbers mapped to their corresponding widget instance post IDs. When
 accessing an item in the array, the `offsetGet()` method can then look-up
 the widget instance data and cache it for future lookups.

 This backwards-compatible shim approach is similar to what @nacin did in
 #20103 for `WP_Theme` (see also [https://vip.wordpress.com/2014/08/26/how-
 wordpress-evolves-full-transcript/ How WordPress Evolves Without Breaking
 Everything]).

 Let's make the widget a first-class citizen in WordPress.

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Ticket URL: <https://core.trac.wordpress.org/ticket/32474>
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