March update on bordeaux.guix.gnu.org

[Christopher Baines <mail@cbaines.net>]

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Hey!

I'm think the last update I sent out was back in April 2023 [1], but
it's coming up to 3 years since bordeaux was added as a default
substitute server [2]. It's scary how much time has passed!

1: https://lists.gnu.org/archive/html/guix-devel/2023-04/msg00319.html
2: https://guix.gnu.org/en/blog/2021/substitutes-now-also-available-from-bordeauxguixgnuorg/

I've finally got around to starting to address the problems with
disappearing nars discussed in [3]. The nar-herder now schedules nars
which it's generated for removal and the time for removal is based on
the TTL in use.

3: https://issues.guix.gnu.org/63634

Related to this, I've added options to the nar-herder to help change the
TTL being used, and reduced the TTL for bordeaux.guix.gnu.org to 10
minutes (from 180 days) [4]. This will at least mean that in the future,
the nar-herder on bordeaux will be able to delete zstd compressed nars
that it's generated more quickly.

4: https://git.savannah.gnu.org/cgit/guix/maintenance.git/commit/?id=1fc5a1af488cb8838c2f196e07a43f37f2fbf509

I'm really unsure about the need/usefulness of narinfo caching in
general, the cost of storing all these narinfos locally is quite high I
think and I don't really know why it's done.

The mishandling of these zstd nars available from bordeaux was the last
thing on my mind blocking proposing to switch the default substitute
server ordering, so I've now gone ahead and done that in [5].

5: https://issues.guix.gnu.org/70028

Obviously the differences to having ci.guix.gnu.org first in the list of
substitute URLs is subtle, but I'm hoping this will help with substitute
speed issues (as discussed in [6]) plus increase the impact of mirroring
work for the bordeaux substitutes in the future.

6: https://lists.gnu.org/archive/html/guix-devel/2023-05/msg00290.html

Apart from that, the main thing on my mind for the next year regarding
bordeaux substitutes specifically is storage space. We're at 90%
capacity on hatysa (one of the two machines storing all the nars) so
this will need looking at shortly. I'd also like to finally get removing
nars that don't relate to the guix master branch happening, as that
should free up a little bit of space at least.

Let me know if you have any comments or questions!

Thanks,

Chris

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