Surely it is at least as hard to find people who know how to write Java without GC?

Presumably you can't use Hotspot so you have to write your own VM too?

Folks with a background in electronic trading (FX, hedge funds, trading firms etc) are familiar with zero-gc Java. London / NY / HK are a good pool of talent in that respect

Yep, I ended up checking their code base. I know a little bit of Java but didn't realise that sun.misc.Unsafe existed, so it does actually look fairly straightforward to create code outside of GC (for anyone reading questdb/std/Unsafe.java seems to be where some allocations are handled). A pain I am sure, but way more manageable than I thought.

It's not necessarily outside of GC, it's that they make great efforts to avoid GC. Such as instantiating all objects at startup and holding references to avoid GC, never using new keyword, avoiding objects in favor of primitives, avoid exceptions, etc.

These systems often restart or do a full "stop the world" GC once per day.

The system is quite different than what most are used to, especially during a trend towards increasingly Functional styles with immutability as a default, etc.

Peter Lawrey[1] has some great posts/talks about his experiences in HFT.

[1] https://github.com/peter-lawrey