I'm confused. Redis is a cache with persistent backing option. This is a database. Have I missed something?
You can also add your own data structures to Redis, not as a form of syntax sugar over KV pairs, but as a dynamic library that you can write in C/C++/Zig/Rust, where you have full control over the in-memory representation.
But that's also another feature AWS takes away from you if you buy elasticache :^)
It's often used as a cache because it does key-value storage in memory well
I consider it to be cache first, "db" second, with true definition of db first being something that can execute SQL or SQL like statements (such as Cassandra's CQL). It's the same reason I don't call Cassandra a cache, although it can achieve the same result.
true definition of db first being something that
can execute SQL or SQL like statements
Additionally, a lot of "toy" databases like Access can execute SQL statements, so the ability to execute SQL statements isn't necessarily a great way to tell what's a "real" database.
In practical terms, I do agree with you -- if somebody in 2023 is referring to "the database" in their app they had darn well better be talking about something robust and ACID-compliant like Postgres or whatever.
Do you have an example of an use case for which using Redis as a database works significantly better than using say Postgres or MySQL?