Aside from your bad math above, the reporter heard million when I said billion. More than 3 billion rows per day. That math is easy enough to come by if you do any math on the rest of the numbers: 400M (Tweets per day) * 4 (replication) = 1.6B rows per day to store the Tweets, plus the same amount for an entry in a timeline. So that's 3.2B right there. And there are a lot of other types of indexes.