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Re: guix-gc

From: Ludovic Courtès
Subject: Re: guix-gc
Date: Tue, 22 Jan 2013 22:56:57 +0100
User-agent: Gnus/5.130005 (Ma Gnus v0.5) Emacs/24.2 (gnu/linux)

Andreas Enge <address@hidden> skribis:

> Am Donnerstag, 10. Januar 2013 schrieb Ludovic Courtès:
>> Nix provides other options that extend this model to something closer to
>> what you say, namely ‘gc-keep-outputs’ (see
>> <http://hydra.nixos.org/build/3676991/download/1/nix/manual.html>.)
>> I guess we should add a guix-daemon option for that.
> If I understand the manual correctly, this is not exactly what I meant. I 
> thought of simply keeping all packages that are needed to build a simple 
> project, such as "hello". Or maybe just keeping gcc, as it takes really 
> very long to build. But indeed, this is less critical once binary downloads 
> from a build farm are possible.

I’ve actually installed or registered roots for such “precious”
packages, which prevents them from being GC’d.

> Another option would be something close to debian's "apt-get autoclean": 
> Keep all the packages that are still available in the sense that they would 
> be built by calls to "guix-build", looping over the output of "guix-package 
> --list-available".

For packages that use ‘gnu-build-system’, the prerequisites are a
superset of (@ (gnu packages base) final-inputs), which includes GCC,
Coreutils, libc, etc.  So you would want to keep those, I guess, right?

OTOH, imagine a hypothetical ‘python-build-system’, whose only implicit
inputs are Python and perhaps Coreutils.  Someone who only installs
Python packages only cares about keeping Python and Coreutils around.

And then, the GC.  The GC only sees derivations, and derivation outputs.
It doesn’t have the slightest idea of which outputs are valuable to the
user, and which aren’t.

So the normal way to address this problem is to tell the GC what’s
important: by installing packages, or by running ‘guix-build --root’.

The Nix daemon options I mentioned above can be used to do something
more: keeping the source tarballs of derivations whose outputs are still

But as you note, all this will be much less of a concern when we can
download pre-built binaries.  Something to get in for 0.2, I guess.  :-)



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