cache_page not cleared via system_cron

It should also be noted that my memcache config is

  'cache_inc' => './sites/all/modules/memcache/memcache.inc',
  'session_inc' => './sites/all/modules/memcache/memcache-session.inc',
  'memcache_servers' => array(
    'cache1:11211' => 'default',
    'cache1:11212' => 'menu',
    'cache1:11213' => 'filter',
    'cache1:11214' => 'page',
    'cache1:11215' => 'views',
    'cache1:11216' => 'content',
    'cache1:11217' => 'form',
    'cache1:11218' => 'session',
    'cache1:11219' => 'users',
  ),
  'memcache_bins' => array(
    'cache_page'    => 'page',
    'cache_menu'    => 'menu',
    'cache_filter'  => 'filter',
    'cache_views'   => 'views',
    'cache_content' => 'content',
    'cache_form'    => 'form',
    'session'       => 'session',
    'users'         => 'users',
  ),

Right, so cache_clear_all() still works for clearing the page and block cache after node saves b/c it calls back on itself with cache_clear_all('*', 'cache_page', TRUE). In the core version this would call cache_clear_all(NULL, 'cache_page') as a mechanism for clearing expired entries. system_cron calls to clear the page cache with cache_clear_all(NULL, 'cache_page') but that call no longer clears expired entries, it lands in no mans land and essentially does nothing.

  FROM: memcache.inc

  if (!isset($cid) && !isset($table)) {
    cache_clear_all('*', 'cache_block', TRUE);
    cache_clear_all('*', 'cache_page', TRUE);  <=========== THIS IS HOW PAGE CACHES GET CLEARED
                                                               NOT THE SAME AS system_cron SO A CRON RUN
                                                               WILL NOT CLEAR CACHED PAGES
    return;
  }
  if (empty($cid) || ($cid == '*' && $wildcard !== TRUE)) {  <===== PASSES THIS TEST B/C CID IS NULL

    // don't do anything if cid is unset. this matches the default drupal behavior...
    if ($wildcard && $cid != '*') {                                       <======= FAILS THIS TEST B/C WILDCARD IS FALSE
      if (variable_get('memcache_debug', FALSE)) {
        // call watchdog, since you probably didn't want to flush the entire bin.
        watchdog('memcache', "illegal wildcard in cache_clear_all - not flushing entire bin. table: $table. cid: $cid", WATCHDOG_WARNING);
      }
    }
    <================ DOES NOTHING AND EXITS
  }
  else if ($cid == '*' || $wildcard === TRUE) {
  ...

FROM memcache.db.inc

  // Default behavior for when cache_clear_all() is called without parameters
  // is to clear all of the expirable entries in the block and page caches.
  if (!isset($cid) && !isset($table)) {
    // Clear the block cache first, so stale data will
    // not end up in the page cache.
    cache_clear_all(NULL, 'cache_block');
    cache_clear_all(NULL, 'cache_page');  <=============== DIFFERENT DEFAULT BEHAVIOR THAN memcache.inc
                                                           BUT EXACTLY THE SAME AS system_cron SO CRON WILL
                                                           RESULT IN CACHE CLEARING FOR PAGES/BLOCK
    return;
  }

  if (empty($cid)) {  <======================== PASSES THIS TEST
    if (variable_get('cache_lifetime', 0)) {  <===============FAILS THIS TEST
      // We store the time in the current user's $user->cache variable which
      // will be saved into the sessions table by sess_write(). We then
      // simulate that the cache was flushed for this user by not returning
      // cached data that was cached before the timestamp.
      $user->cache = time();

      $cache_flush = variable_get('cache_flush', 0);
      if ($cache_flush == 0) {
        // This is the first request to clear the cache, start a timer.
        variable_set('cache_flush', time());
      }
      else if (time() > ($cache_flush + variable_get('cache_lifetime', 0))) {
        // Clear the cache for everyone, cache_flush_delay seconds have
        // passed since the first request to clear the cache.
        db_query("DELETE FROM {". $table ."} WHERE expire != %d AND expire < %d", CACHE_PERMANENT, time());
        variable_set('cache_flush', 0);
        // Note there is no memcache flush here.
        // Items are cached in memcache with an expiry equal to cache_lifetime
        // and memcache will expire these automatically.
      }
    }
    else {
      // No minimum cache lifetime, flush all temporary cache entries now.
      // Note, however, that memcache does not have the ability to discern
      // between CACHE_PERMANENT and CACHE_TEMPORARY items. So having no
      // minimum cache lifetime means that all CACHE_PERMANENT items are
      // lost here, too. To avoid that, set a minimum cache lifetime.
      dmemcache_flush($table);     <==============================FLUSHES CACHE HERE
      db_query("DELETE FROM {". $table ."} WHERE expire != %d AND expire < %d", CACHE_PERMANENT, time());
    }
  }
  else {

I hope the above makes sense. :)

Bump. Wondering if anyone has thoughts in this one, this is a pretty major bug if you don't use DB backed memcache.

The bug, as I'm experiencing it, is that the Drupal page cache is supposed to clear cached pages on cron runs. The memcache only version of cache.inc does not do this (but the db backed version does) thus once a page is cached it will never get flushed from the cache unless there is another event that causes cache purging (like a node save for example). The memcache-only version does not seem to expire these entries by itself, I have done some extensive testing of this. It does not seem right that the 2 different versions of cache.inc provided by this module function differently on cron runs.

How does the memcache-only version of cache.inc expect/handle the expiration of cached pages when no minimum ttl is set?

Thanks for helping.