When this is 'on', a request will not go through the
redirector if all the helpers are busy. If this is 'off' and the
redirector queue grows too large, the action is prescribed by the
on-persistent-overload option. You should only enable this if the
redirectors are not critical to your caching system. If you use
redirectors for access control, and you enable this option,
users may have access to pages they should not
be allowed to request.
Enabling this option sets the default url_rewrite_children queue-size
option value to 0.