From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: inputs vs. native-inputs vs. propagated-inputs
Date: Sat, 18 Jun 2016 21:24:06 +0200
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In-Reply-To: <20160617233433.GA10924@jasmine> (Leo Famulari's message of "Fri,
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To: Leo Famulari <leo@famulari.name>
Cc: Hartmut Goebel <h.goebel@crazy-compilers.com>, help-guix <help-guix@gnu.org>

Leo Famulari <leo@famulari.name> skribis:

> I _think_ that `gc --references` works by querying the database for a
> list of references in the store item you give it as an argument. I think
> that the information in the database is created after building, by
> scanning the files of the package's output in /gnu/store, looking for
> strings that appear to be paths in /gnu/store. I say "I think" because I
> am not sure. I don't understand that part of the code very well yet.

That=E2=80=99s 100% correct!  :-)  Namely, =E2=80=98guix gc --references=E2=
=80=99 makes an RPC to
the daemon, which then looks things up in the database (see the =E2=80=98Re=
fs=E2=80=99
table in nix/libstore/schema.sql.)

Scanning for references indeed happens at the end of a successful build,
in =E2=80=98scanForReferences=E2=80=99 in libstore/references.cc.  Since sc=
anning is
expensive (I/O-intensive), the result is stored in the database.

Ludo=E2=80=99.