How do applications like twitter handle notifications at scale.
For example @BarackObama has 131.3 million followers. When he tweets, how is that notification sent to all 131.3 million followers.
I supposed you could load all 131.3 million followers one page at a time and update some state point to that new tweet, but it seems highly inefficient and I would imagine it would take some long that you would have to be mindful of people following / unfollowing during this process.
Are there any better ways?