Schema: Add an index to `wp_options.autoload`.

Most sites will be unaffected by this change, but those with a large number of rows in `wp_options`, only a small number of which have `autoload` set, will see a significant performance improvement.

Sites with a large number of rows in `wp_options`, with many of them having `autoload` set will unfortunately see a performance penalty on top of the already very slow queries they're running, but this should be the minority of cases.

Props DanBUK.
Fixes #24044.


git-svn-id: https://develop.svn.wordpress.org/trunk@45805 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/schema.php

@@ -144,7 +144,8 @@ CREATE TABLE $wpdb->options (
 	option_value longtext NOT NULL,
 	autoload varchar(20) NOT NULL default 'yes',
 	PRIMARY KEY  (option_id),
-	UNIQUE KEY option_name (option_name)
+	UNIQUE KEY option_name (option_name),
+	KEY autoload (autoload)
 ) $charset_collate;
 CREATE TABLE $wpdb->postmeta (
 	meta_id bigint(20) unsigned NOT NULL auto_increment,

src/wp-includes/version.php

@@ -20,7 +20,7 @@ $wp_version = '5.3-alpha-45282-src';
  *
  * @global int $wp_db_version
  */
-$wp_db_version = 45744;
+$wp_db_version = 45805;
 
 /**
  * Holds the TinyMCE version