Slow queries when i edit page on the backend.

hi guys,

i have noticed on my query monitor that a query runs slow, over 6 seconds which it should be doing it much less then 0.001.

the query is as follows;

SELECT DISTINCT meta_key
FROM wphq_postmeta
WHERE meta_key NOT BETWEEN ‘_’
AND ‘_z’
HAVING meta_key NOT LIKE ‘\\_%’
ORDER BY meta_key
LIMIT 30

the error is coming from this template wp-admin/includes/template.php:613

which is this;

* @param array|null $keys Pre-defined meta keys to be used in place of a postmeta query. Default null.
* @param WP_Post $post The current post object.
*/
$keys = apply_filters( ‘postmeta_form_keys’, null, $post );

if ( null === $keys ) {
/**
* Filter the number of custom fields to retrieve for the drop-down
* in the Custom Fields meta box.
*
* @since 2.1.0
*
* @param int $limit Number of custom fields to retrieve. Default 30.
*/
$limit = apply_filters( ‘postmeta_form_limit’, 30 );
$sql = “SELECT DISTINCT meta_key
FROM $wpdb->postmeta
WHERE meta_key NOT BETWEEN ‘_’ AND ‘_z’
HAVING meta_key NOT LIKE %s
ORDER BY meta_key
LIMIT %d”;
$keys = $wpdb->get_col( $wpdb->prepare( $sql, $wpdb->esc_like( ‘_’ ) . ‘%’, $limit ) );
}

if ( $keys ) {
natcasesort( $keys );
$meta_key_input_id = ‘metakeyselect’;
} else {
$meta_key_input_id = ‘metakeyinput’;
}

any guidance or help would be great. as i am really confused on what to do, never had the issue or problem before.

Marc

thanks in advance