David Kimura PRO said over 7 years ago on Redis Basics :

I'll usually use the same database but different namespaces. However, I will put services on their own database. For example, if I were using Redis for caching as well as storing the User Sessions, I would put caching on db 0 and the sessions on db 1. This makes it easier to flush all of the stored cache without wiping out the user sessions (or vice versa).