Re: Guix pull: avoiding "Computing Guix derivation"

[Ryan Sundberg]

Hi Edouard, I have couple of ideas for you, which may help with your deployment 
process:

1) if possible, mount /gnu on a btrfs filesystem with zstd compression enabled. 
This will let you fill up at least 3x of your physical disk space because the 
store compresses very well.

2) for production servers you should try using `guix deploy` to push rather 
than pull profiles. This will offload most of the process to the machine 
pushing the deployment.

With regards to multi user profiles, if this is a typical server (not a 
terminal/shell server) I wonder why you need to have per user profiles at all. 
I only say this because I am not sure about running `guix deploy` on an 
individual user basis.

Sincerely,
Ryan Sundberg

May 13, 2024 8:08:35 AM Edouard Klein <edou@rdklein.fr>:

> Hi Guix,
> 
> First, I'd like to apologize for not having taken the time to answer
> those who helped me on a previous guix performance issue (with
> containers), the reason is tied to the topic of this email: the store
> has eaten all the space of my server, and solving that takes precedence
> over everything else, because no space == no services.
> 
> So, I need to clear some space, and to do that I need to have every user
> run guix pull (and by that I mean root will sudo -u $user guix pull),
> then update all of their profiles, and then guix gc
> --delete-generations.
> 
> This ought to turn deduplication up to 11, and enjoy a reduced store
> size.
> 
> I've already solved the cache size problem:
> mount -t overlay overlay -o \
> lowerdir="/root/.cache/guix",upperdir="/home/$user/.cache/guix-overlay",workdir="/home/$user/.cache/guix-workdir"
>  \
> "/home/$user/.cache/guix"
> 
> Then
> bindfs --mirror=$user /home/$user/.cache/guix /home/$user/.cache/guix
> 
> This lets root (who just ran guix pull) share its cache with every user,
> and avoid blasting away 700MB of disk space in every $HOME to reproduce
> the cache.
> 
> However, now, I'm facing the previously addressed problem of guix pull
> being slow and hungry:
> https://www.mail-archive.com/guix-devel@gnu.org/msg66442.html (Guix pull 
> speed)
> https://yhetil.org/guix/87h6mwf4u3.fsf@lapenas.dev/T/ (guix pull
> performance)
> 
> On my server, in order to run guix pull, I have to stop all other
> services otherwise I run out of ram.
> 
> Then, one root has pulled, I need to wait 4 minutes /per user/ for guix
> pull to finish its "Computing Guix derivation" step.
> 
> I would like to know two things, one is for the sake of knowledge, and
> the other is to solve the problem at hand:
> 
> - Why is this step not substitutable ? The inputs are known, a hash can
> be derived, a substitute server could be queried for an output of that
> hash ? What am I missing ? Does the guix derivation not end up in the
> store ? What makes it so special that it can't be served by a substitute
> server ?
> 
> - Is there a way (even a very dirty one, like hand copying stuff accross
>   /var/guix/profiles/per-user/*/current-guix) I can stop paying this 4
>   minutes per user price ? As I said, this is downtime on my server, as
>   I need to stop all other services to let guix pull finish.
> 
> Thanks in advance.
> 
> Sorry for beating a dead horse, it's just that I can't scale anything up
> until I solve these performance issues. Sure I could rent a bigger
> server, but that's just kicking the can down the road.
> 
> 
> Cheers,
> 
> Edouard.