Depends how much you have to cache and how much speed you really need from it.

I like Redis a lot, but for things in the start I'm not sure the juice is always worth the squeeze to get it setup and manage another item in teh stack.

Luckily, search is something that has been thought about and worked on for a while and there's lots of ways to slice it initially.

I'm probably a bit biased though from past experiences from seeing so many different search engines shimmed beside or into a database that there's often an easier way in the start than adding more to the stack.