Fwiw, he has been providing quite a lot of transparency in his posts to this community. He's shared his hardware config in detail, posted maintenance posts with brief descriptions of what he's doing, and replied to comments around specific config tweaks. I haven't catalogued a list of links, but I've seen him do all of these things in the last 48h. It's easy to imagine that all these things could be compiled in real time into a how-to, but it's a pretty big deal just to keep the lights on right now, and pretty difficult to understand whether tweaks that helped your setup are generally applicable or only situationally useful and happen to perform well for your specific setup.
I'm sure we will see more high-performance Lemmy guides in the future, but at this point no one has more than 36h of experience with high-performance Lemmy. Give them a minute to catch up.
Saying this without any knowledge of lemmy's backend... Large, high user count databases with (very quickly) growing demand take more power than generally expected. At a certain point, throwing money at the problem is the solution.
I respect anyone working with any amount of databases. Just my selfhosted operation made me realize how fucking complicated and stupid but nessasary databases are