Re: updating list of substitutes

[Ludovic Courtès]

Pjotr Prins <address@hidden> skribis:

> The list of substitutes gets downloaded every time I do someting:
>
>   substitute: updating list of substitutes from 'http://hydra.gnu.org'...   
> 4.6%
>
> and it is slow. Am I doing something wrong?

No!  Slowness is a longstanding issue of hydra.gnu.org, a poor little
VM.  I hope we can address it soon!  See
<https://lists.gnu.org/archive/html/guix-devel/2015-10/msg00172.html>.

> It appears to me that if the list does not change it should not be
> downloaded.

It’s not downloaded “every time.”

When building a package FOO, Guix looks for substitutes for FOO and its
prerequisites (those not already available locally.)  It maintains in
/var/guix/substitute/cache a cache of those lookups.

Positive caches (for substitutes that are available) expire after 36h;
negative caches (substitutes that are missing) expire after 3h.

See (guix scripts substitute) for details; look for ‘ttl’.

Ludo’.