Early days (~50K users)

Twitter's signature move

Fan-out on write — except for the famous

Rather than assemble each timeline the moment it is read, Twitter writes every new tweet straight into all of its followers' timelines up front, so reading a timeline is instant. The exception is celebrities: fanning one tweet out to a hundred million followers would be a hundred million writes, so those accounts' tweets are merged in at read time instead. The real design is the hybrid — cheap fan-out for ordinary users, on-the-fly assembly for the few everyone follows.

Build it yourself

Now try building one of these architectures from a blank canvas — you're scored on the services you place and how you wire them.