Re: Building and caching old Guix derivations for a faster time machine

[Simon Tournier <zimon.toutoune@gmail.com>]

Hi Ricardo,

On Fri, 10 Nov 2023 at 10:29, Ricardo Wurmus <rekado@elephly.net> wrote:

> to me the biggest downside of using “guix time-machine” is that it has
> to do a lot of boring work before the interesting work begins.  The
> boring work includes building Guix derivations for the given channels,
> most of which have long been collected as garbage on ci.guix.gnu.org.
>
> It would be helpful, I think, to more aggressively cache these
> derivations and their outputs, and to go back in time and build the
> derivatinons for past revisions of Guix.  I would expect there to be a
> lot of overlap in the produced files, so perhaps it won’t cost all that
> much in terms of storage.

I agree.  And it rings a bell about a discussion on the private
guix-sysadmin mailing list, subject: Backup for substitutes.

Back in 2022, Alexandre from Univ. Montpellier was proposing to store
the artifacts the project would like to keep for a longer term.  Well, I
do not know what is the current status.

That’s said, I am in favor:

 1. keep all the derivations and their outputs required by Guix itself.
 
 2. keep all the outputs for some specific revisions; say v1.0, v1.1,
 v1.2, v1.3, v1.4, and some other chosen points in time.

About #1, it will help when running “guix time-machine”.  About #2, it
will help with concrete issues as time-bombs when running “guix
time-machine -- shell”

The questions are: which server?  who maintain? :-)

Cheers,
simon