Re: A 2025 NewYear present: make dpkg --force-unsafe-io the default?

[Aurélien COUDERC <coucouf@coucouf.fr>]

Le mercredi 1 janvier 2025, 20:13:35 UTC+1 Ahmad Khalifa a écrit :
> On 01/01/2025 18:27, Aurélien COUDERC wrote:
> > Here’s a quick « benchmark » in a sid Plasma desktop qemu VM where I had a snapshot of up-to-date sid from Nov 24th, upgrading to today’s sid :
> > 
> > Summary:
> >    Upgrading: 658, Installing: 304, Removing: 58, Not Upgrading: 2
> >    Download size: 0 B / 1 032 MB
> >    Space needed: 573 MB / 9 051 MB available
> > 
> > # time apt -y full-upgrade
> > 
> > real    9m49,143s
> > user    2m16,581s
> > sys     1m17,361s
> > 
> > # time eatmydata apt -y full-upgrade
> > 
> > real    3m25,268s
> > user    2m26,820s
> > sys     1m16,784s
> > 
> > That’s close to a *3 times faster* wall clock time when run with eatmydata.
> 
> The second upgrade hasn't been written back at all. For up to 30 
> seconds, if your machine loses power and for example grub.{cfg,efi} or 
> shim.efi was updated, you can't boot at all. Not to mention Kernel 
> panics still happen.

Yes but no. :)
It’s true that I should have included a final sync in the measurement but in practice it makes no difference because writing however many 100s of MB in a single sync is almost instantaneous.

Here’s a new run with a final sync :

# time eatmydata apt -y full-upgrade ; time sync

real    3m25,116s
user    2m26,947s
sys     1m17,962s

real    0m0,109s
user    0m0,002s
sys     0m0,000s

> Surely, we can all agree dpkg should at least do a single 'sync' at the 
> end? Perhaps this would be a more realistic comparison?
> # time (eatmydata apt -y full-upgrade; sync)

Yes I never said the contrary, the kind of guarantees that dpkg and/or apt are providing are highly valuable.

It would be better if it was not coming at such a high cost.


Happy hacking,
--
Aurélien