Also that may introduce race condition. Think about when several concurrent requests trying to update the same option at the same time.

We need a faster way to store this, and separate each group's data so we reduce running into race condition.

After some thoughts, there's another idea -- if we are not frequently flushing the whole memcached server now, maybe it's good idea to use a separate key/value to store each of group/timestamp?

Then we don't have to touch MySQL and improve speed.