Get random item from sorted set in Redis

Question

I was needed to implement set of items with individual expiration, so I used zsetwith score of expiration timestamp. Now I want to get random item from range of not expired items, or at least from all items in set. How can I do it?

Can I get min and max rank of range and random rank in between of it via LUA scripting?

Redis version: 5.0.2

Answer 1

I solve this via following script:

-- KEYS[1] - set key
-- ARGV[1] - seed timestamp

local count = redis.call('ZCARD', KEYS[1]) 
if count ~= 0 then
    math.randomseed(ARGV[1]) 
    local rank = math.random(0, count - 1) 
    local range = redis.call('ZRANGE', KEYS[1], rank, rank)
    return range[1]
else
    return ''
end

And because I search among all items I do sanitization from expired items every n seconds.