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From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: updating list of substitutes
Date: Mon, 12 Oct 2015 19:03:51 +0200
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In-Reply-To: <20151012060607.GA11012@thebird.nl> (Pjotr Prins's message of
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To: Pjotr Prins <pjotr.public12@thebird.nl>
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Pjotr Prins <pjotr.public12@thebird.nl> skribis:

> On Mon, Oct 12, 2015 at 01:15:01AM -0400, Mark H Weaver wrote:
>> The phrase "the substitute list" suggests a single, complete list of all
>> available substitutes, but there is no such list.  Instead, quoting
>> Ludovic above:
>>=20
>>   "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."
>>=20
>> So, if you build package BAR immediately after building FOO, a different
>> set of substitutes is queried, and typically that involves more lookups
>> (unless FOO runtime-depends on BAR).
>>=20
>> Does that make sense?
>
> Right. So, why don't we have one list for every build? That would save
> connecting to the one single server every time and be less fragile.

Again, it=E2=80=99s not =E2=80=9Cevery time,=E2=80=9D as we=E2=80=99ve seen=
.  :-)

I=E2=80=99m not sure what you have in mind with =E2=80=9Cone list for every=
 build.=E2=80=9D

Quoth
<http://www.gnu.org/software/guix/manual/html_node/Substitutes.html>:

  Substitutes can be anything resulting from a derivation build (see
  Derivations).

Each derivation has a number of dependencies, and for each dependency
that is not already available locally, we want to know whether
substitutes are available.  This is the list we=E2=80=99re talking about.  =
It
depends on what=E2=80=99s available in the local store, the state of the lo=
cal
substitute cache, etc.

Having said that, I=E2=80=99m all for fewer network accesses.  When we have=
 a
new front-end with more disk space, we can hopefully have it retain
build products for longer, and thus increase the TTL.

In the meantime, anyone can run =E2=80=98guix publish=E2=80=99 and pass the=
 URL via
=E2=80=98--substitute-urls=E2=80=99.

HTH!

Ludo=E2=80=99.