Memcached provides a custom session handler that can be used to store user sessions in memcache. A completely separate memcached instance is used for that internally, so you can use a different server pool if necessary. The session keys are stored under the prefix memc.sess.key., so be aware of this if you use the same server pool for sessions and generic caching.
If you want to use 'memcacheD' extention not 'memcache' (there are two diffrent extentions) for session control, you should pay attention to modify php.ini
Most web resource from google is based on memcache because It's earlier version than memcacheD. They will say as following
session.save_handler = memcache
session.save_path = "tcp://localhost:11211"
But it's not valid when it comes to memcacheD
you should modify php.ini like that
session.save_handler = memcached
session.save_path = "localhost:11211"
Look, there is no protocol indentifier
This extension supports Session-locking!