If you are interested in hyper-scale event processing but you want to learn it from first principles, I strongly recommend following Martin Thompson's talks. Here is an example of one on cluster consensus:

> https://www.youtube.com/watch?v=GFfLCGW_5-w

and another on event log architecture:

> https://www.youtube.com/watch?v=RlwO6CJbJjQ

After digging through all of this material and playing around with LMAX Disruptor & Raft, I have been able to develop a really good understanding of how to build these sorts of systems on my own. Fun constraints like "Only one thread actually mutates anything, and its the same one over and over" make for incredibly elegant implementation opportunities. Not having to constantly hunt down exotic thread-safe data structures means that you can focus on building actual value.

Latency is the biggest devil you will dance with in this arena, so almost everything you do will be oriented around mitigating that effect. Latency both at the network and inside the CPU/memory/storage. It applies at every level.