GNU bug report logs - #22990
Grafts leads to inefficient substitute info retrieval

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Ludovic Courtès <ludo <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#25137: closed (repeated updating list of substitutes during
 install)
Date: Mon, 30 Mar 2020 02:36:51 +0000

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Your message dated Sun, 29 Mar 2020 15:41:24 +0200
with message-id <87tv271dob.fsf <at> gnu.org>
and subject line Re: bug#22990: Grafts leads to inefficient substitute info retrieval
has caused the debbugs.gnu.org bug report #22990,
regarding repeated updating list of substitutes during install
to be marked as done.

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help-debbugs <at> gnu.org.)


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From: Dave Love <fx <at> gnu.org>
To: bug-guix <at> gnu.org
Subject: repeated updating list of substitutes during install
Date: Thu, 08 Dec 2016 13:50:07 +0000

During a package install (of guix itself) I see "updating list of
substitutes" messages repeated through the install, not just at the
start.  Is that as it should be?  I expected guix to use a recent cached
version.

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From: Ludovic Courtès <ludo <at> gnu.org>
To: 22990-done <at> debbugs.gnu.org
Subject: Re: bug#22990: Grafts leads to inefficient substitute info retrieval
Date: Sun, 29 Mar 2020 15:41:24 +0200

Hi younger self!

ludo <at> gnu.org (Ludovic Courtès) skribis:

> As of right now (v0.9.0-2007-g66a30a3), ‘graft-derivation’ works either by:
>
>   1. Fetching substitute info about the things being built so that it
>      can determine its references, which in turns allows it to determine
>      whether they need to be grafted.
>
>   2. Building stuff, as a last resort, so that it can determine its
>      references.
>
> Case #1 is hopefully going to be the most common.
>
> The problem with #1 is that when building a profile, we do one
> ‘package-derivation’ call for each package in the profile, which
> translates in one ‘graft-derivation’ call for each relevant package¹,
> which translates into one ‘references/substitutes’ call for each.
>
> Concretely, what this means is this:
>
>   $ guix package -u
>   substitute: updating list of substitutes from 'http://mirror.guixsd.org'... 100.0%
>   substitute: updating list of substitutes from 'http://mirror.guixsd.org'... 100.0%
>   substitute: updating list of substitutes from 'http://mirror.guixsd.org'... 100.0%
>   substitute: updating list of substitutes from 'http://mirror.guixsd.org'... 100.0%
>   substitute: updating list of substitutes from 'http://mirror.guixsd.org'... 100.0%
>   substitute: updating list of substitutes from 'http://mirror.guixsd.org'... 100.0%
>   substitute: updating list of substitutes from 'http://mirror.guixsd.org'... 100.0%
>   […]
>   The following files would be downloaded:
>
> Each of the initial “updating list” message corresponds to an HTTP
> request for a single narinfo file, which can take around 1 second.

This is finally fixed with commit
710854304b1ab29332edcb76f3de532e0724c197, as discussed earlier this
week¹.  \o/

The solution is simpler and more orthogonal than what was envisioned
earlier in this thread, which is nice.

I also potentially addresses other uses of “dynamic dependencies”
elsewhere in the code base, such as ‘remote-eval’ calls in ‘guix
deploy’.

Feedback welcome!

Ludo’.

¹ https://lists.gnu.org/archive/html/guix-devel/2020-03/msg00337.html

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