The problem isn't hello world, it's the start-up time of big jars. My experience tells me that JVM start-up time on actual large software projects is a real issue in practice. But I haven't used Bazel in particular; I'd be more interested in numbers for that than numbers for hello world.

> As for ZFS, what do you mean? [...] It’s just Linus’s overprotective stance against mixing two open-source licenses that makes it unmergable into the kernel

Haha, that's not right. The problem is that ZFS's license, the CDDL, is (intentionally) incompatible with the GPL, so you can't link CDDL code against GPL code. It's not just an issue with making it part of the main Linux tree either, it's probably not even legal for distros to even ship a ZFS kernel module, since that has to link against Linux's GPL code (according to common interpretations of the licenses; Canonical notably disagrees).

And let me repeat that this mess was intentional on the part of Sun when they made the CDDL (see https://en.wikipedia.org/wiki/Common_Development_and_Distrib...), and it remains intentional on the part of Oracle as they choose to keep ZFS under the CDDL.

The mechanism which prevents Linus from merging ZFS into the kernel, and the mechanism which prevents distros from shipping ZFS out of the box, is the exact same mechanism which prevents Linus from merging any other GPL-incompatible code or distros from shipping any other GPL-incompatible kernel modules.

Nothing is stopping any individual from grabbing the OpenZFS source code and linking it against their Linux kernel; that's legal. Oracle is just doing its best to prevent people from combining OpenZFS and Linux into one package and distributing the result.