From: Chris Marusich <cmmarusich@gmail.com>
To: Lukas Gradl <lgradl@openmailbox.org>
Cc: help-guix <help-guix@gnu.org>
Subject: Re: inputs vs. native-inputs vs. propagated-inputs
Date: Sun, 10 Jul 2016 14:23:45 -0700 [thread overview]
Message-ID: <877fctrxum.fsf@gmail.com> (raw)
In-Reply-To: <87ziqe8xyg.fsf@openmailbox.org> (Lukas Gradl's message of "Tue, 21 Jun 2016 08:37:27 -0500")
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Lukas Gradl <lgradl@openmailbox.org> writes:
> ludo@gnu.org (Ludovic Courtès) writes:
>
>> Lukas Gradl <lgradl@openmailbox.org> skribis:
>>
>>> ludo@gnu.org (Ludovic Courtès) writes:
>>>
>>>> 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’s 100% correct! :-) Namely, ‘guix gc --references’ makes an RPC to
>>>> the daemon, which then looks things up in the database (see the ‘Refs’
>>>> table in nix/libstore/schema.sql.)
>>>>
>>>> Scanning for references indeed happens at the end of a successful build,
>>>> in ‘scanForReferences’ in libstore/references.cc. Since scanning is
>>>> expensive (I/O-intensive), the result is stored in the database.
>>>
>>> Sorry, this might be a dumb question, I don't quite understand the
>>> concept of these references. Why are references important? Shouldn't
>>> every store item know which other store-items are related to it from the
>>> "inputs"-field in its definition? Why is it necessary to keep track of
>>> the references?
>>
>> The “references” of a store item are its run-time dependencies, a subset
>> of the ‘inputs’ etc. fields, which are themselves the compile-time
>> dependencies.
>>
>> If those run-time dependencies were not inferred automatically by the
>> daemon, we’d have to maintain them individually, and this would be
>> error-prone and imprecise.
>>
>> Run-time dependency information is what allows Guix to know which
>> substitutes need to be downloaded when installing from substitutes, and
>> it’s what allows the garbage collector to determine which store items
>> are “live”, and which ones are not.
>>
>
> OK, Thank you for the explanation, this makes more sense to me now!
>
> Best,
> Lukas
If you are curious, there is a more detailed explanation of "references"
in Eelco Dolstra's PhD thesis, "The Purely Functional Software
Deployment Model", available here:
https://nixos.org/%7Eeelco/pubs/phd-thesis.pdf
You'll find more information about Nix here, much of which applies to
Guix also:
http://nixos.org/docs/papers.html
You'll find more links about Guix here:
https://www.gnu.org/software/guix/contribute/
And this repo contains talks etc. about Guix:
http://git.savannah.gnu.org/cgit/guix/maintenance.git/tree/
--
Chris
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prev parent reply other threads:[~2016-07-10 21:24 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-12 9:07 inputs vs. native-inputs vs. propagated-inputs Hartmut Goebel
2016-06-12 12:38 ` 宋文武
2016-06-12 15:50 ` Hartmut Goebel
2016-06-12 19:53 ` Leo Famulari
2016-06-17 20:49 ` Hartmut Goebel
2016-06-17 23:34 ` Leo Famulari
2016-06-18 19:24 ` Ludovic Courtès
2016-06-19 3:57 ` Lukas Gradl
2016-06-19 13:44 ` Ludovic Courtès
2016-06-21 13:37 ` Lukas Gradl
2016-07-10 21:23 ` Chris Marusich [this message]
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