If you are running a wordpress blog you might experience a very high number of “hits” to “/wp-admin/admin-ajax.php”. This can cause a very high load on the server, and if you are running your blog on a shared hosting platform, your hosting provider might even disable the script.
To resolve this you can make the changes below to ensure the script exits quickly if no action is supplied with the file request.
Change this
15 define(‘WP_ADMIN’, true);
16
17 require_once(‘../wp-load.php’);
18
19 if ( ! isset( $_REQUEST['action'] ) )
20 die(‘-1′);
21
22 require_once(‘./includes/admin.php’);
To This
15 define(‘WP_ADMIN’, true);
16
17 if ( ! isset( $_REQUEST['action'] ) )
18 die(‘-1′);
19
20 require_once(‘../wp-load.php’);
21
22 require_once(‘./includes/admin.php’);
For more info see this page: http://core.trac.wordpress.org/changeset/15606
or this http://wordpress.org/support/topic/wp-adminadmin-ajaxphp-with-some-27767-hits-on-this-file