When does it make sense to use Redis instead of SQL/Postgres?
never
It's not used instead of relational database.
>>56273104
I know, which is why I'm asking for the specific use cases.
>>56273092
never, you use Redis and a another SQL.
Redis is a simple key-value db, really really fast. It is good for stuff like checking if a cookie is valid (ie. is there a reference to this cookie in the db?)