pagecache

Description:
This patch is designed to prevent cache stampedes when updating pages in the Drupal page cache. When serving cached pages, logic checks the timestamp of the cached page -- if older than the global timestamp we try to grab a lock. Only one user can grab the lock for a given page at a time. If the user fails to grab the lock, a stale version of the cached page is returned. Once the page is rebuilt, the new version is returned on subsequent requests.

Description:
Re-order Drupal core's bootstrap process so anonymous pages can be served from an external cache (such as memcache) without hitting the database.

Drupal's default bootstrap order is as follows:

    DRUPAL_BOOTSTRAP_CONFIGURATION
    DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE
    DRUPAL_BOOTSTRAP_DATABASE
    DRUPAL_BOOTSTRAP_ACCESS
    DRUPAL_BOOTSTRAP_SESSION
    DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE

This patch changes it as follows:

    DRUPAL_BOOTSTRAP_CONFIGURATION
    DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE
    DRUPAL_BOOTSTRAP_SESSION