I've been reading up quite a bit on distributed database and compute technologies like Spanner/MapReduce as well as some interesting blog posts on scaling out of Facebook/Twitter/Netflix.

That got me wondering how even "harder" problems - like Visa's payments system, or the global stock exchange network, are implemented. In these applications, the problem is inherently planet-scale, correctness is of utmost importance, and latency is still very, very important.

I haven't been able to find much online on how applications like these are designed, verified and implemented, so any help will be appreciated!