[Nix-dev] duplicate packages?

[Guillaume Maudoux (Layus)]

Le 04/08/16 à 10:57, Roland Koebler a écrit :
> Hi,
>
> I have Nix running on Debian with the default channel [*], and I noticed,
> that -- although I only have a few packages installed -- many dependencies
> are installed several times. I would like to understand, why.
>
> [*] https://nixos.org/channels/nixpkgs-unstable nixpkgs
First of all, there may be old derivations in the store.
You should look for duplicates in the output of
nix-store -qR ~/.nix-profile, not in the store directly.

Because there can exist many generation of you profile in the store.
>
>
> 1. Many packages are installed several times with the same version
>    number, e.g.:
>
>    2pa9z1h2m0pyik4hr1ikfl6jvdg8j4pb-acl-2.2.52
>    8c5s33f5mzfn9z3yhjprxnxzl19dg7p2-acl-2.2.52
>    sk0b1r840b686zc2m8mzyw8yyq1aymqh-acl-2.2.52
>
>    4vgjwvgf24jl3czzksai6mwsklvhgs4k-attr-2.4.47
>    8z667vv1agvpd3iknmk94j0ix6bv413i-attr-2.4.47
>    m8qi9jrz51lqn7x0mifa9kpwpsp3b7dq-attr-2.4.47
>
>    fxkm8r0vpv88ld82jz0a00sjvh342wfl-avahi-0.6.31
>    p817p19niamk0f06r5wvqvdqnym96r7w-avahi-0.6.31
>    5wi7ja71s4wdjkzfghc4lkwrwc45fnf9-avahi-0.6.32
>
>    d20f169ryps7ds2qak0r5n1f4hhxr80h-bash-4.3-p42
>    d44582rghk696yw704sh5nbvbpnm69iv-bash-4.3-p42
>    xag5ayq906w9zhlxs8wayv4kvpiyqphq-bash-4.3-p42
>
>    0y480sh5b4hny3iq8fy3ppha0zllxxaw-boehm-gc-7.2f
>    bw1p8rairfwv2yif2g1cc0yg8hv25mnl-boehm-gc-7.2f
>    f24zx1r39kalz01q9kw7zcg1ngj7w2db-boehm-gc-7.2f
>
>    98s2znxww6x7h2ch7cj1w5givahxmdna-glibc-2.23
>    phffgv3pwihmpdyk8xsz3wv8ydysch8w-glibc-2.23
>
>    ...
>
>    I know that different build-inputs result in different hashes, but I
>    would have expected a more homogeneous structure in nixpkgs (e.g.
>    only one acl-2.2.52 in nixpkgs and not several ones), so that
>    I don't need e.g. 3 times acl-2.2.52 or bash-4.3-p42.
You only get an homogeneous structure if you update all your packages at
the same time.
Doing nix-env -u will "[o]nly upgrade a derivation to newer versions [as
t]his is the default."

>From a tree with

+--- package a v1
|    `--- 2pa9z1h2m0pyik4hr1ikfl6jvdg8j4pb-acl-2.2.52
`--- package b v1
     `--- 2pa9z1h2m0pyik4hr1ikfl6jvdg8j4pb-acl-2.2.52

Running nix-env -u may update package a and not package b.
As the new package a is built in the new nixpkgs, it comes with a new
acl (same version, but different as probably one dependency changed).

You get two different acl in your system.

+--- package a *v2*
|    `--- *8c5s33f5mzfn9z3yhjprxnxzl19dg7p2*-acl-2.2.52
`+--- package b v1
     `--- 2pa9z1h2m0pyik4hr1ikfl6jvdg8j4pb-acl-2.2.52

To avoid this, you can upgrade packages with other flags like --eq.
Look an nix-env --upgrade manual section :

       --lt
           Only upgrade a derivation to newer versions. This is the default.

       --leq
           In addition to upgrading to newer versions, also “upgrade” to
derivations that have the same version. Version are not a unique
           identification of a derivation, so there may be many
derivations that have the same version. This flag may be useful to force
           “synchronisation” between the installed and available
derivations.

       --eq
           Only “upgrade” to derivations that have the same version.
This may not seem very useful, but it actually is, e.g., when there is a new
           release of Nixpkgs and you want to replace installed
applications with the same versions built against newer dependencies (to
reduce
           the number of dependencies floating around on your system).

       --always
           In addition to upgrading to newer versions, also “upgrade” to
derivations that have the same or a lower version. I.e., derivations may
           actually be downgraded depending on what is available in the
active Nix expression.

>    Is this because I use nixpkgs-unstable, and everything is moving
>    there, and is this reduced in the NixOS-release-channels?
>    Or is there some other reason?
The problem comes from how nix-env updates packages, but is less visible
if you follow a stable branch.

>
> 2. Is there a way to clean this up?
>    Either in the repository or locally?
>    Or is there a reason why this should not be cleaned up?
See above flags.
>
> 3. Is there a simple way to find the nix-expression (e.g.
>    default.nix-file) of an installed package / a path in
>    the nix-store?
>    And is there a way to know which directory in the nix-store
>    belongs to which .drv-file?
Not that I know of. There was a discussion at NixCon about that, but no
implementation yet.
Your best bet is to `grep` for the name in nixpkgs tree.

To find the .drv of a derivation, provided it has not yet been
garbage-collected, you can call `nix-store --query --deriver
/nix/store/derivation`
>
>
> thanks,
> Roland
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