Caching and Rendering
The {% cache %} tag will only write to the database.

You don't provide many details, so all I can do is offer some general advice.

I'd double check how you're using the {% cache %} and make sure that you're not over-caching your data or caching lots of static data that might not need it.

You can always through something like Varnish/Fastly in front of Craft to help with template caching.

You can tell Craft to use things like memcache with the cacheMethod config setting, but that only affects Craft's non-template data caches.