Another option would be to use zstd for the final compression of the image (zstd is already a dependency as it decompresses the rootfs image).

What do you think? cc @lovesegfault @AmineChikhaoui

zstd -T4:

• output size: 614908377 (decrease of 2%)
• duration: 10 seconds (95% faster) 🤯

real	0m10.069s
user	0m36.025s
sys	0m1.431s

It seems that zstd is even in the Debian stable, so this change might be worth considering.

@prusnak Hi!

I agree that using bzip2 is counterproductive as it's extremely slow, especially on more constrained HW. I think pbzip is okay as a stop-gap, but just using zstd is a much better approach that will benefit even single-core systems.

FWIW: I've suggested in the past that we move all our compression to zstd as it has amazing ratio and speed.

I will gladly rework the PR to use zstd instead if that's what we really want.

IIRC the last time I tried to do this there was some discussion on whether or not the output format, in this case the compression algo, of a drv constituted a "public interface" or not; in which case changing it can't be done without further consideration as it breaks things.

IMO: The benefits are significant enough to be worth it, but it needs to be added to the release notes.

Okay, let's close this and pursue a bigger change (zstd) in another PR: #85947