Redis set vs hash

Question

In many Redis tutorials (such as this one), data is stored in a set, but with multiple values combined together in a string (i.e. a user account might be stored in the set as two entries, "user:1000:username" and "user:1000:password").

However, Redis also has hashes. It seems that it would make more sense to have a "user:1000" hash, which contains a "username" entry and a "password" entry. Rather than concatenating strings to access a particular value, you just access them directly in the hash.

So why isn't it used as much? Are these just old tutorials? Or do Redis hashes have performance issues?

Answer 1

Redis hashes are good for storing more complex data, like you suggest in your question. I use them for exactly that - to store objects with multiple attributes that need to be cached (specifically, inventory data for a particular product on an e-commerce site). Sure, I could use a concatenated string - but that adds unneeded complexity to my client code, and updating an individual field is not possible.

You may be right - the tutorials may simply be from before Hashes were introduced. They were clearly designed for storing Object representations: http://oldblog.antirez.com/post/redis-weekly-update-1.html

I suppose one concern would be the number of commands Redis must service when a new item is inserted (n number of commands, where n is the number of fields in the Hash) when compared to a simple String SET command. I haven't found this to be a problem yet on a service which hits Redis about 1 million times per day. Using the right data structure to me is more important than a negligible performance impact.

(Also, please see my comment regarding Redis Sets vs. Redis Strings - I think your question is referring to Strings but correct me if I'm wrong!)