Is getting data back from Redis SETS faster or more performant than HSETS?

Question

I currently have a scenario where we are using REDIS to store string field-value pairs within a hashed set HSET.

The original reasoning behind using hashed sets instead of just sets is ease of retrieving the records using HSCAN inside a GUI Search Bar as opposed to just SCAN because it's easier to get the length of a hash to use in the COUNT field.

I read in the Redis documentation that both GET and HGET commands execute with O(1) time complexity, but a member of my team thinks that if I store all the values inside a single key then it basically returns the entire hash during HGET instead of the singular field-value that I need.

So for a made up but similar example:

• I have a Redis instance with a single Hashed Set called users.
• The hashed set has 150,000 field:value pairs of username:email

If when I execute hget users coolguy, is the entire hash getting returned or just the email for user coolguy?

Answer 1

First of all, HSET is not a hash set, it creates a hash table. The mechanism behind the hash table and set (which is indeed a hash set) in redis is the same, the difference is mainly that the hash table has values.

To answer your question:

If when I execute hget users coolguy, is the entire hash getting returned or just the email for user coolguy?

Just the email for that user. You can also use HMGET to get the emails of multiple users at once. It's O(1) for each user you fetch, or O(n) for n users.