In rolling out our real time bidding infrastructure, we were faced with the task of syncing data for every user we could possibly target across four regions. We have on the order of hundreds of millions of users, and tens of thousands of writes per second. Not only do we have to deal with the daunting task of writing this data out in real time, the bidding system has a hard cap of 100ms for every bid request, so we need strong guarantees on read performance.
