zlacker

Did they actually need to know Bieber's friend count both accurately and in real time?

I would expect that for top Twitter accounts like his, you could get a very good approximation by logging events that increment or decrement the friend count, and using the rates those events are occurring and the last known exact friend count to forecast the current friend count. That would not be exact, but I bet you could get it close enough that users would not see anything off about it.

>>tzs+(OP)
Yes they made Storm for this

>>tzs+(OP)
Ha, I always joke that Twitter is a good example of why one should avoid distributed systems. Every often, you see it showing the wrong number of friends, tweets, likes, etc. I don't care, I suppose some people care about such metrics.

>>segmon+uT
That's the essence of the CAP theorem. You can have two of three - consistency, availability, and partition tolerance. Sometimes it makes sense to choose availability over consistency.