Integration between Drupal and Memcached with the following features:

• An API for using Memcached and the PECL Memcache or Memcached libraries with Drupal.
• Memcache backends for the following systems (all drop-in):
• Caching (memcache.inc)
• Sessions (memcache-session.inc)
• Locking (memcache-lock.inc)
• A module that provides a comprehensive administrative overview of Drupal's interaction with Memcached and stats.
• A set of tests that can be run to test your memcache setup.

For requirements, installation requirements, and common troubleshooting issues, see the documentation.

Note that Drupal core 7.8 has a bug which conflicts with memcache, but which was fixed in 7.9, you should upgrade to the latest stable core release.