Caching paginated results, purging on update - how to solve?

Question

I\'ve created a forum, and we\'re implementing an apc and memcache caching solution to save the database some work.

I started implementing the cache layer with keys like

Answer 1

One possible solution is not to paginate the cache of threads in a forum, but rather put the thread information in to Forum::getThreads|$iForumId. Then in your PHP code only pull out the ones you want for that given page, e.g.

$page = 2;
$threads_per_page = 25;
$start_thread = $page * $threads_per_page;

// Pull threads from cache (assuming $cache class for memcache interface..)
$threads = $cache->get("Forum::getThreads|$iForumId");

// Only take the ones we need
for($i=$start_thread; $i<=$start_thread+$threads_per_page; $i++)
{
    // Thread display logic here...
    showThread($threads[$i]);
}

This means that you do have a bit more work to do pulling them out on each page, but now only have to worry about invalidating the cache in one place on update / addition of new thread.