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

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

Ricardo Wurmus <rekado@elephly.net> skribis:

> 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.
>
> What do you think?

I agree.  The ‘guix publish’ TTL¹ at ci.guix was increased to 180 days
following <https://issues.guix.gnu.org/48926> in 2021.  That’s still not
that much and these days and right now we have 84 TiB free at ci.guix.

I guess we can afford increasing the TTL, probably starting with, say,
300 days, and monitoring disk usage.

WDYT?

For longer-term storage though, we’ll need a solution like what Simon
described, offered by university colleagues.  I’m not sure why this
particular effort stalled; we should check with whoever spearheaded it
and see if we can resume.

Thanks,
Ludo’.

¹ That’s the time-to-live, which denotes the minimum time a substitute
  is kept.  Anytime a substitute is queried, its “age” is reset; if
  nobody asks for it, it may be reclaimed after its TTL has expired.