MySQL has a query cache which stores results of queries, though it's not very useful if you have frequent writes. Linux and other operating systems tend to use

MySQL has a query cache which stores results of queries, though it's not very useful if you have frequent writes. Linux and other operating systems tend to use any free memory for disk cache which will end up caching the whole database if needed. Innodb has a key cache. Memcached probably helpful on the database server but it's really designed to be ran somewhere else so that database server has as much memory as possible of it's own.