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]);