id	summary	reporter	owner	description	type	status	priority	milestone	component	version	severity	resolution	keywords	cc
20236	Improper testing of cache retrievals causes wasted queries.	andy		"`wp_cache_get()` can retrieve values such as the empty array which is considered false by the `!` test. The following function is incorrect because it will always ignore the cache and repeat the `get_col` and `wp_cache_add` when the cache contains the empty array. This occurs on sites which have no pages.

{{{
function get_all_page_ids() {
        global $wpdb;

        if ( ! $page_ids = wp_cache_get('all_page_ids', 'posts') ) {
                $page_ids = $wpdb->get_col(""SELECT ID FROM $wpdb->posts WHERE post_type = 'page'"");
                wp_cache_add('all_page_ids', $page_ids, 'posts');
        }

        return $page_ids;
}
}}}

The cache check should be written with an understanding of the return type of `$wpdb->get_col()` (array). Here it is with the check fixed:

{{{
function get_all_page_ids() {
	global $wpdb;

	$page_ids = wp_cache_get('all_page_ids', 'posts');
	if ( ! is_array( $page_ids ) ) {
		$page_ids = $wpdb->get_col(""SELECT ID FROM $wpdb->posts WHERE post_type = 'page'"");
		wp_cache_add('all_page_ids', $page_ids, 'posts');
	}

	return $page_ids;
}
}}}

Patch 1 fixes this occurrence. Please keep this ticket open until all similar occurrences are found and fixed."	defect (bug)	closed	normal	3.4	Cache		normal	fixed	has-patch