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Re: inputs vs. native-inputs vs. propagated-inputs

From: Chris Marusich
Subject: Re: inputs vs. native-inputs vs. propagated-inputs
Date: Sun, 10 Jul 2016 14:23:45 -0700
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Lukas Gradl <address@hidden> writes:

> address@hidden (Ludovic Courtès) writes:
>> Lukas Gradl <address@hidden> skribis:
>>> address@hidden (Ludovic Courtès) writes:
>>>> Leo Famulari <address@hidden> 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/  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:

You'll find more information about Nix here, much of which applies to
Guix also:

You'll find more links about Guix here:

And this repo contains talks etc. about Guix:


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