One of the features of WordPress is the ease of applying dropdown menus with access to posts & pages.

Applying menus in the header is a simply matter of including the following lines of code in header.php

wp_nav_menu(array(
‘items_wrap’ => ‘%3$s’,
‘depth’ => 3,
‘theme_location’ => ‘header-menu’,
‘container’ => false ));

However, this simple routine is pretty slow for complex or crowded menus and can result in a bottleneck as the page loads.
One solution is to cache the menus (which we presume chane infrequently), using WordPress’s “transient” command.

Effectively we test to see if we have a copy of the menu or whatever element in the cache.
If not, we add it to the cache, however if it does exist in the cache we grab it from there rather than creating it.

$cached_menu=get_transient(‘the_header_menu’);
if(false === $cached_menu){         
      $cached_menu =  wp_nav_menu(array( ‘items_wrap’ => ‘%3$s’, ‘depth’ => 3, ‘theme_location’ => ‘header-menu’, ‘container’ => false, ‘echo’ => false ));                 
set_transient(‘the_header_menu’, $cached_menu, 3600*5);    
} 
    echo $cached_menu;