CODEWITHSUNDEEP
redis
Nabil A.
Nabil A.

Reputation: 3400

Atomic update a redis set only if element is not present

I know barely anything about redis, except it is in-memory and fast. But I have a case I consider using it.

I have a system, that may have a huge number of users (500k+ may up to a few million) and I want to do a unique check for email adresses across all users. I consider using redis to maintain a set of all email adresses to do the uniquness check. So I asked my self, is it possible to do something like

if(!set.contains(email)) add email

as an atomic operation and then get a simple result I can handle, just like failure or success.

This code/command should be callable from concurrent code.

If there is a different tool that would fit my needs better, I am open to suggestions.

Upvotes: 2

Views: 977

Answers (1)

Nick Bondarenko
Nick Bondarenko

Reputation: 6351

Use SET datatype for that:

Redis Sets are an unordered collection of Strings. It is possible to add, remove, and test for existence of members in O(1) (constant time regardless of the number of elements contained inside the Set).

Redis Sets have the desirable property of not allowing repeated members. Adding the same element multiple times will result in a set having a single copy of this element. Practically speaking this means that adding a member does not require a check if exists then add operation.

So just use

SADD emails [email protected]

Upvotes: 5

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