this lua script is used to in redis. it will set to the key if the value is bigger than the `updateat:{timestamp}`, if no udpateat founded update as normal

update_if_bigger.lua

local a = redis.call('get',KEYS[1]);
if a and a:find("^updateat:") ~= nil then
    -- this key already update by anther thread. so we test
    if tonumber(string.sub(a, 10, string.len(a))) <= tonumber(KEYS[2]) then
        return redis.call('set',KEYS[1], KEYS[3]);
    end
    return;
end
return redis.call('set',KEYS[1], KEYS[3]);

127.0.0.1:6379> set foo updateat:100

redis-cli --eval /tmp/a.lua foo 120 message --> success

redis-cli --eval /tmp/a.lua foo 80 message --> failed

redis-cli --eval /tmp/a.lua foo2 80 message --> success, since no foo2