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

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

Hi Maxim,

On Thu, 30 Nov 2023 at 08:28, Maxim Cournoyer <maxim.cournoyer@gmail.com> wrote:

> I'd like to have a single archive type as well in the future, but I'd
> settle on Zstd, not lzip, because it's faster to compress and
> decompress, and its compression ratio is not that different when using
> its highest level (19).

When running an inferior (past revision), some past Guile code as it was
in this past revision is launched.  Hum, I have never checked: the
substitution mechanism depends on present revision code (Guile and
daemon) or on past revision?

Other said, what are the requirements for the backward compatibility?
Being able to run past Guix from a recent Guix, somehow.


>>  1. Keep for as longer as we can all the requirements for running Guix
>>  itself, e.g., “guix time-machine”.  Keep all the dependencies and all
>>  the outputs of derivations.  At least, for all the ones the build farms
>>  are already building.
>>
>>  2. Keep for 3-5 years all the outputs for specific Guix revision, as
>>  v1.0, v1.1, v1.2, v1.3, v1.4.  And some few others.
>
> That'd be nice, but not presently doable as we can't fine tune retention
> for a particular 'derivation' and its inputs in the Cuirass
> configuration, unless I've missed it.

That’s an implementation detail, a bug or a feature request, pick the
one you prefer. ;-)

We could imagine various paths for these next steps, IMHO.  For
instance, we could move these outputs to some specific stores
independent of the current ones (ci.guix and bordeaux.guix).  For
instance, we could have “cold” storage with some cooking bakery for
making hot again, instead of keeping all hot.  For instance, we could
imagine etc. :-)

Well, I do not have think much and I just speak loud: Cuirass (and Build
Coordinator) are the builders, and I would not rely on them for some NAR
“archiving“, instead maybe “we” could put some love into the tool
nar-herder.  Somehow, extract specific NAR that the project would like
to keep longer than the unpredictable current mechanism.

Cheers,
simon