zlacker

There was a fun high-scalability article around their 'fan-out' approaches to disseminating tweets by popular users etc : http://highscalability.com/blog/2013/7/8/the-architecture-tw... .

When I was working on something with similar technical requirements I also came across this paper (http://jeffterrace.com/docs/feeding-frenzy-sigmod10-web.pdf) that outlined the approach in a more 'formal' manner.