Re: updating list of substitutes

[Pjotr Prins]

On Sun, Oct 11, 2015 at 08:39:32PM +0200, Ludovic Courtès wrote:
> 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>.

Looking forward to that :)

> > 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.

The weird thing is that most times I install a new package it does a
lookup. Only rarely it does not. According to the TTL it should then
check every 3hrs at most? Somehow I don't understand why we need to
download the substitute list every time I install a new package. Not
even Debian does that ;) I would think that the list of (prebuild,
right?) substitutes is only updated when some build is triggered.
Could be there are builds triggered while I am installing software
forcing a new list every time. Is that it?

I understand we have a list of prebuilt packages and that the list can
change. But maybe I am too simplistic in my assumptions. I'll look
into that code tomorrow.

Pj.