CODEWITHSUNDEEP
hashredis
saadlulu
saadlulu

Reputation: 1395

Key value pairs Vs hashes for large amounts of data

Lets assume in a system where we have about 10 million users. we need to cache those users objects after retrieval from the database into redis.

Now the question is would we store those JSON objects into a key value pairs something like "user_1" or a more appropriate solution would be having them all into the same hash "users" and the hash key would be the user ID "1 in this case"

I assume having key-value pairs would take much more memory than a hash, but what about the performance?

Upvotes: 2

Views: 2862

Answers (2)

DDupont
DDupont

Reputation: 451

3 years late, but given @Matias' comment on sharding with Redis Cluster it is worth noting that the unit of sharding is the key name. That means that all values in a hash will end up on the same server. So for millions of users, the global key space would allow for sharding, but not a hash.

Upvotes: 1

Matías Fidemraizer
Matías Fidemraizer

Reputation: 64923

Since both global key space and hashes are hash tables, access time has complexity O(1). Performance shouldn't be an issue in both cases.

BTW, I would take a look at this official Redis docs' article about memory optimization. Its first paragraph states:

Since Redis 2.2 many data types are optimized to use less space up to a certain size. Hashes, Lists, Sets composed of just integers, and Sorted Sets, when smaller than a given number of elements, and up to a maximum element size, are encoded in a very memory efficient way that uses up to 10 times less memory (with 5 time less memory used being the average saving).

Also, you said:

we have about 10 million users.

Then, either if you use globak key space or hashes, you should take a look at sharding with Redis Cluster. Probably this way you should be able to even optimize more your scenario.

Upvotes: 2

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