Multiple keys pointing to a single value in Redis (Cache) with Java

Question

I want to store multiple keys with a single value using jedis (Redis cache) with Java.

I have three keys like user_1, driver_10, admin_5 and value = this is user, and I want to get value by using any one key among those three.

Lemire

Could you clarify what exacly is your key? Is it [user_10,driver_5] including brackets? Which redis java client are you using? jedis, jredis? (don't know any "jdis") – Acanthocephalan

I want to add multiple key which is pointing single value suppose i have three keys like user_1,driver_10,admin_5 and value = "this is user" and i want to get value by using any one key among three – Lemire

Answer 1

Having multiple keys point to same value is not supported in Redis for now, see issue #2668.

You would need a workaround.

Some ideas below, possibly obvious or stupid :)

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Maybe have an intermediate key:
- user_10 → id_123
- driver_5 → id_123
- id_123 → data_that_you_dont_want_to_duplicate

You could implement that logic in your client code, or in custom Lua scripts on server, and have your client code use those scripts (but I don't know enough about that to provide details).

If you implement the indirection logic on client side, and if accesses are unbalanced, for example you would access data via user key 99% of the time, and via driver key 1% of the time, it might be worth avoiding 2 client-server round trips for the 99% case. For this you can encode redirections. For example, if first character is # then the rest is the data. If first character is @ then the rest is the actual key.

• user_10 → #data_that_you_dont_want_to_duplicate
• driver_5 → @user_10

Acanthocephalan

I want to add multiple key which is pointing single value suppose i have three keys like user_1,driver_10,admin_5 and value = "this is user" and i want to get value by using any one key among three – Lemire

OK then I think I understood correctly, and the first sentence of my answer is relevant: that is not supported currently, so you can go comment on the linked github issue, or consider workarounds. – Acanthocephalan

Your workaround makes absolute sense. It's super brilliant not stupid – Pleurisy

Suppose I wanted to invalidate #data_that_you_dont_want_to_duplicate. I could invalidate user_10, but then how does the driver_5 -> @user_10 K-V get cleaned up in redis? – Renae

Answer 2

Here is a Lua script that can save on trafic, and pull the data in one call:

eval "return redis.call('get',redis.call('get',KEYS[1]))" 1 user-10

The above will return the request data.

Robertaroberto

how do you ensure that both the keys are present in the same shard/cluster? – Touchy

you can't with that, but it is not its purpose anyway. if you need something like that, you should read redis.io/topics/cluster-spec in which hash tags are explained. – Enrage