Individual set member expiry, inspired by https://github.com/antirez/redis/issues/135

expiring_sorted_set.rb

require 'redis'

#
# The drawback with this approach is old members are deleted as you add new, creates a bit of overhead.
# The whole set expires, using normal redis expiration, if you don't add anything until the last member was added
#
class ExpiringSortedSet
  attr_reader :key

  def initialize(args)
    @key    = args[:key]
    @redis  = args[:redis]
    @expiry = args[:expiry]
  end

  def add(v)
    created_at = Time.now.to_i
    expire_old_set_members(created_at)
    expire_key
    @redis.zadd @key, created_at+@expiry, v
  end

  def members
    @redis.zrangebyscore @key, Time.now.to_i, "+inf"
  end

  private
  def expire_key
    @redis.expire @key,@expiry
  end

  def expire_old_set_members(since)
    @redis.zremrangebyscore @key, "-inf", since-1
  end
end

p "running timed test"
# make a set with key test:1, set members should expire within 5 seconds
s = ExpiringSortedSet.new(:key => "test:1", 
                          :redis => (redis=Redis.new(:host => "localhost")), 
                          :expiry => 5)
redis.del s.key
s.add(1)

sleep 3
puts s.members, "^ should be 1"

s.add(2)
puts s.members, "^ should be 1, 2"

sleep 3      # 1 expires here
puts s.members, "^ should be 2"

s.add(3)
puts s.members, "^ should be 2, 3"

# if set isn't accessed in the next 5 seconds, the whole key expires
sleep 6
puts s.members, "^ should be empty"