Custom Fields Meta Box: Define Meta Keys for Performance

custom-fields-meta-keys.php

<?php
/**
* Plugin Name: Custom Fields Meta Box: Define Meta Keys for Performance
* Plugin URI: http://www.wpzinc.com/
* Version: 0.0.1
* Author: WP Zinc
* Author URI: http://www.wpzinc.com
* Description: Explicitly define the Meta Keys to display in the Custom Fields > Add New Custom Field > Name <select> dropdown, to save WordPress performing a potentially expensive and slow query. 
*/

/**
 * Defines the Meta Keys to display in the <select> dropdown.
 *
 * If null is returned, WordPress will perform a DB query to fetch all unique
 * meta keys from the Post Meta table, which can be a slow and expensive
 * query if the WordPress installations contains a lot of post meta data.
 *
 * @since   0.0.1
 *
 * @param   array   $meta_keys  Meta Keys
 * @param   WP_Post $post       WordPress Post
 * @return  array               Meta Keys
 */
function custom_fields_meta_box_meta_keys( $meta_keys, $post ) {

    // Define the meta keys that you want to return
    // You must specify at least one
    $keys = array(
        'key1',
        'key2',
    );
    
    // Stop editing
    return $keys;

}
add_filter( 'postmeta_form_keys', 'custom_fields_meta_box_meta_keys', 10, 2 );