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

From: Lukas Gradl
Subject: Re: inputs vs. native-inputs vs. propagated-inputs
Date: Sat, 18 Jun 2016 22:57:56 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

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?

Thank you!

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