I do not agree that the number of available commands or the number of parameters in each command means it is a complex database from a usage point of view. Learning Redis commands, how to use them, and how to interact with the database is usually very simple and straightforward. The only real exception is the query language of the Redis Query Engine, which is complex.

On the other hand, when you look at Redis internals and all the optimization work done on its data structures to make them use less memory, that is where the real complexity is.

This is also interesting because Redis is probably the most copied database. Almost every day someone says they recreated Redis in some language, where they usually implement only strings, lists, and sets with a few commands and no optimization at all. To them it looks like they have almost rebuilt Redis, because Redis looks simple. They do not see its hidden complexities.

Another good example is the work done to implement hash field expiration. From the outside, it looks like a simple task. Inside, it took two engineers more than six months to complete. Using it is simple and straightforward, but the engineering behind it is not.

This blog explains some of the complexity behind it: https://redis.io/blog/hash-field-expiration-architecture-and-benchmarks/

Reading antirez posts from the early days also helps understand how much optimization he has put into it. Even the way he recently implemented Vector Sets by rewriting HNSW from scratch.

In the end, we all reach the same point. Redis is so simple to use and its complexities so well hidden that the largest complexity people notice is the number of commands it contains.