title: Memcached, Redis, or Couchbase
body: <p>I have a Debian server with about 16GB RAM that I'm using with nginx and several heavy mysql databases, and some custom php apps.  I'd like to implement a memory cache between Mysql and PHP, but the databases are too large to store everything in RAM.  I'm thinking a LRU cache may be better so far as I research.  Does this rule out Redis?  Couchbase is also a consideration.</p>