Question: (newbie here) if we assume that with 350 million keys for the 64GB ram server we have reached the peak of it's capacity, if we double the number of keys, do we have to get new hardware, like a second server or double the ram?

Or is it something simpler? Like storing the current keys on disk (somehow) and keep going with the server as it is.

To rephrase my question: keeping all in ram... is "all" like ALL ??? Would this solution work for the "real" twitter, with the billion twits, if 350 million keys were created every hour?