title: Whats the best way to manage keys (in memcache ) to prevent stale cached values?
body: <p>Ive recently implemented memcache on my site which has been under heavy mysql load (mysql was as optimized as I could make it). It solved all my load issues, and site is running beautifully.</p>
  
  <p>The problem that Im facing now is stale cached values. I have 1hr auto expiration times on most  pages, and Im also deleting the key when the value in the DB chnages, but Im having difficulty keeping track and efficiently clearing out all the keys. </p>
  
  <p>On some pages, its trivial. I can make the key be item_id (item_4653 for example), and when the data for it is updated, or the item is deleted, the key is cleaned out.</p>
  
  <p>But on most pages, I take the script filename + querystring, md5 it, and use that as the key in memcache. This is especially useful for complex urls (which are very common). </p>
  
  <p>For example I have the following page loaded.</p>
  
  <p>index.php?search_keywords=<em>good</em>&amp;search_section=1&amp;sort=release&amp;page=2</p>
  
  <p>It will contain a list of items, which will be fetched from memcache. Another user then submits an item, which has "<em>good</em>" in its title, and it happens to be in the range of values, where it would appear on page 2, except it will not appear there, until the cache is refreshed. What makes this even more complicated, is that the newly added item will also appear on index.php?sort=newest, as well as index.php?category=some_category?page=1 and etc. Each 1 of those will have a unique key (md5 of the script name + query string).</p>
  
  <p>So the newly added item might appear on dozens of pages, if they were fetched from a live DB, but it wont be visible on any of them until the stale cache is updated. The only option is to wait for the item to expire automatically.</p>
  
  <p>This problem becomes even more pronounced  on my forum (custom coded), where the values HAVE to be updated on demand, for all possible cached page combinations. Lets say I have 4 page thread, and I notice 3 spam posts on page 2. After deleting them, page 2 is rebuilt, but then it also has to rebuild pages 3 and 4, otherwise there will be duplicate posts on newly rebuild page 2, and old page 3. Thats just 1 example to..... there are dozens of these scenarios. </p>
  
  <p>Any ideas?</p>