Options, Meta APIs: Prevent excessive notoptions key lookups.

When the `notoptions` key does not exist in a persistent object cache, it was requested hundreds of times until the first not-option is written.

This commit improves performance by setting the value to an empty array to prevent non-existent `notoptions` key from triggering multiple key lookups.

Follow-up to [4855], [14515].

Props tillkruess, dd32, spacedmonkey.
Fixes #56639.

git-svn-id: https://develop.svn.wordpress.org/trunk@54345 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/option.php

@@ -164,6 +164,12 @@ function get_option( $option, $default = false ) {
 		// Prevent non-existent options from triggering multiple queries.
 		$notoptions = wp_cache_get( 'notoptions', 'options' );
 
+		// Prevent non-existent `notoptions` key from triggering multiple key lookups.
+		if ( ! is_array( $notoptions ) ) {
+			$notoptions = array();
+			wp_cache_set( 'notoptions', $notoptions, 'options' );
+		}
+
 		if ( isset( $notoptions[ $option ] ) ) {
 			/**
 			 * Filters the default value for an option.