Oh... I just found this in the high scalability web site (http://highscalability.com/scaling-twitter-making-twitter-10000-percent-faster http://highscalability.

Oh... I just found this in the high scalability web site (http://highscalability.com/scaling-twitter-making-twitter-10000-percent-faster http://highscalability.com/scaling-twitter-making-twitter-10...): Update 6: Some interesting changes from Twitter's Evan Weaver: everything in RAM now, database is a backup; peaks at 300 tweets/second; every tweet followed by average 126 people; vector cache of tweet IDs; row cache; fragment cache; page cache; keep separate caches; GC makes Ruby optimization resistant so went with Scala; Thrift and HTTP are used internally; 100s internal requests for every external request; rewrote MQ but kept interface the same; 3 queues are used to load balance requests; extensive A/B testing for backwards capability; switched to C memcached client for speed; optimize critical path; faster to get the cached results from the network memory than recompute them locally.