collection.php is passed a collection_id and page number and displays iitems belonging to a the collection matching the collection_id. Collections are paged.

All collections use the same template so each page needs to be identified uniquely identified so that the appropriate cached page can retrieved. This is done by creating a cache identifier from the collection_id and page variables.

When a page is accessed a cache identifier is generated and the cache is checked to see if there is an existing cached page. If the cached page does exist the page is returned from the cache, if not then the page needs to generated and displayed. Page generation may involve template complication and database access and processing, this is avoided if the page exists in cache.

The cached pages expire automatically after after 1 hour (can be set) or can be cleared manually.

This second type of caching (content caching) requires some thought as well as an understanding of the data to be able to successfully implement. The input required to create each page is used to generate a cache identifier and identify the cached page.