I have a wordpress installation (latest version) running on a debian server with memcached and php5-memcached installed (memcache appears on phpinfo()), but W3 Total Cache doesn’t seem to recognize it, the compatibility test reports the extension as not installed and doesn’t offer memcaced as an option in the various cache configurations.
PHP is running as FastCGI if that’s important.
How can I get memcache to work with W3TC?
At the time of this writing, W3TC only recognizes the php5-memcache (vs. php5-memcached) PHP client for memcached memory object caching system/software.
Hence the “Memcache extension: Installed” in W3TC compatibility test for memcached.
Memcached being useful and efficient as a caching method for database and/or object user/data caching via W3TC, even on a single server setup, besides APC or Zend Opcode (PHP 5.5 core).
having php-memchached installed doesn’t mean that you have memcached installed. memcached is a software by itself that should be installed.
In any case if you ask such a basic question about memcache then you don’t need it, and should use APC or xcache for object caching which will give you much better improvement then using memcache (memcached is best used in multi server environment with some kind of load balancing and from your question it doesn’t sound like that is your configuration).