I've sent out PR#4313 to address the slowness issue: https://github.com/NixOS/nixpkgs/pull/4313

On Sun, 28 Sep 2014, [email protected] wrote:

After studying pkgs/build-support/replace-dependency.nix I'm prepraring a preliminary patch for it that should make the computation a zillion times faster.

The dry-run thing not being a dry run is still a bit of a mystery to me, but replace-dependency.nix does do things that are a little strange such as "builtins.unsafeDiscardStringContext".

On Thu, 25 Sep 2014, Ricardo M. Correia wrote:

 On Wed, Sep 24, 2014 at 11:34 PM, Peter Simons <[email protected]> wrote:
       If you are worried about Bash CVE-2014-6271 (you should) and don't
       want
       to wait for Hydra to re-build the world, then check out

         https://github.com/NixOS/nixpkgs/pull/4257#issuecomment-56727114

       to see how to replace the bash binary in your running system without
       triggering re-builds.


 This does appear to work (thanks!), but I'm having some issues with it.
 Namely, when I run "nixos-rebuild dry-run" on my laptop, instead of taking
 3 seconds to finish, now it takes more than 65 minutes (!). It seems to be
 CPU-bound during the
 whole time. Also, take into account my laptop a relatively fast CPU - a
 quad-core i7.

 My Hydra server also took around 65 minutes to evaluate the expressions of
 the 4 machines in my network (I believe usually it doesn't take more than
 a couple of minutes).

 In my laptop, this is the process which seems to be taking 100% CPU during
 the whole time:

 root     16031 83.6  5.8 507344 471848 pts/1   R+   14:16  49:29
 /nix/store/fxik1nhqc4dkb72wl5cgb4fxxxlcrlfz-nix-1.7/bin/nix-instantiate
 --add-root
 /tmp/nix-build.jHT5_9/derivation --indirect -A system <nixpkgs/nixos>

 I know this feature is just a temporary workaround, but it's also a bad
 user experience. From a user perspective, it seemed like the process
 simply got stuck in an infinite
 loop.
 In contrast, compare this to apt-get, which doesn't take more than a
 couple of minutes to install a security fix...

 Also, I'm not sure if this is expected, but when I first tried to run
 "nixos-rebuild dry-run" with this workaround applied, it started to
 download and compile bash even
 though the man page of nixos-rebuild specifically says:

        dry-run
            Simply show what store paths would be built or downloaded by
 any of the operations above.

 Still, thanks for this feature because even though it's slow, it's still a
 lot better than waiting for everything to rebuild!





--
Russell O'Connor                                      <http://r6.ca/>
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''
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