How did you use Redis: as a database or as a cache?

Redis is often used both as a cache and as a database, depending on the project requirements.

• As a cache Redis is used for storing temporary data with quick access, such as results of complex queries, user sessions, data from a database to reduce load.
• As a database Redis can be used for storing structured data in memory with the possibility of persistence to disk (RDB or AOF), allowing it to be used as the main storage for applications with high speed requirements.

In my experience, Redis was more often used as a cache to speed up service operations, for example, caching query results to an SQL database or storing sessions. But Redis was also used as a primary store for some services with simple data structures, where high performance and low latency are important.