What an excellent post, one of the best on 1BRC I've come across so far. Big shout-out to Marko for participating in the challenge, making a strong push for clarifying corner cases of the rules, and sharing his experiences in this amazing write-up!
Thanks for the praise Gunnar, but we all owe it to you for organizing it, and especially sticking through thick and thin when it took off, and needed lots of attention to evaluate everyone and maintain a level playing field!
The last part of the article raises an interesting question for me. What is the fastest, mostly fault tolerant implementation that could be created? So something that runs on say 10 different versions of the input, each of which has had up to 20 characters from the standard ASCII set inserted, replaced or removed randomly in the input file. So we'd be mostly looking for "data corruption" fault tolerance vs hardened against malicious input. How much can you still "out optimize" the compiler and JVM if you can't throw away all the safety?