Hardly changing data on persistent aplications: wut do?

For persistent web applications, is it recommended to store hardly changing values in build-in variables? Should I set up a memory database (such as Redis) to store those values? Or a memory cache?

For example: configuration files will hardly change, and if they do, it's because you did it manually. Any thoughts?

Another example, since we are in a text board. Storing board information in variables, so you can query faster its configuration.