function wc_get_product_ids_on_sale() {
	// Load from cache.
	$product_ids_on_sale = get_transient( 'wc_products_onsale' );

	// Valid cache found.
	if ( false !== $product_ids_on_sale ) {
		return $product_ids_on_sale;
	}

	$data_store          = WC_Data_Store::load( 'product' );
	$on_sale_products    = $data_store->get_on_sale_products();
	$product_ids_on_sale = wp_parse_id_list( array_merge( wp_list_pluck( $on_sale_products, 'id' ), array_diff( wp_list_pluck( $on_sale_products, 'parent_id' ), array( 0 ) ) ) );

	set_transient( 'wc_products_onsale', $product_ids_on_sale, DAY_IN_SECONDS * 30 );

	return $product_ids_on_sale;
}