modify cache expiration of existing full page cache hole punch

Question

I'd like to punch a hole in the full page cache for the top menu of a site. While digging through some Enterprise code, I see that the top menu has an existing hole punched:

//  app/code/coe/Enterprise/PageCache/etc/cache.xml
<catalog_navigation>
    <block>page/html_topmenu</block>
    <name>catalog.topnav</name>
    <placeholder>TOPMENU</placeholder>
    <container>Enterprise_PageCache_Model_Container_Catalognavigation</container>
    <cache_lifetime>86400</cache_lifetime>
</catalog_navigation>

However, I'd like to change the cache_lifetime to be much shorter (1 second). What is the best way to modify the cache_lifetime without modifying core code?

Answer 1

I believe that if you declare a custom module as <depends> on <Enterprise_PageCache/> and create a cache.xml file which contains the following, you will effectively override the core cache_lifetime value:

<?xml version="1.0"?>
<cache>
    <catalog_navigation>
        <cache_lifetime>1</cache_lifetime>
    </catalog_navigation>
</cache>