Why do I see Memcache errors in the browser, terminal, or logs?

Drupal Starter Kits come with built-in configuration for memcache that is disabled by default. Not all Drupal sites need memcache, and not all Drupal sites behave well with memcache. When memcache and Drupal misbehave, it’s almost always because of custom code or scaling issues with multisite. To make this easy to resolve without a code deploy, Drupal Starter Kits leverage a server-level toggle to enable or disable its integration with the memcached daemon.

• Acquia Cloud Enterprise - to enable memcache for ACE, you must set an environment variable. For more information, see Creating customer environment variables from the user interface.

  The variable is ENABLE_MEMCACHED and the value should be ‘1’. To disable, either set the value to ‘0’, or delete the variable.

• Site Factory - to enable memcache for ACSF, an Acquian needs to select the Enable Memcache checkbox for the applicable Site node. Disabling memcache is as simple as reversing the checkbox state. By default, ACSF has only one memcache server for each Factory, which all sites share. The default memory is fairly small. Therefore, a small number of sites in a Factory with memcache enabled will quickly cause memcache to overflow and cause more evictions than successful cache queries, which in turn will cause Drupal to slow down or go offline entirely. Acquia urges caution when implementing memcache for Drupal Starter Kits sites in ACSF.

When enabling or disabling Drupal Starter Kits integration with memcache, you might occasionally see a Drupal WSOD, which can be resolved by rebuilding the cache through Drush or admin UI. Therefore, Acquia does not recommend enabling or disabling memcache during high traffic.