[Nix-dev] Nix 0.12 released

[Eelco Dolstra]

Hi,

I'm pleased to announce the availability of a new stable release of the
Nix package manager.  Release 0.12 can be found at

  http://nixos.org/releases/nix/nix-0.12/

*** Release notes ***

The release notes can also be found at
http://nixos.org/releases/nix/nix-0.12/release-notes.

  * Nix no longer uses Berkeley DB to store Nix store metadata. The principal
    advantages of the new storage scheme are: it works properly over decent
    implementations of NFS (allowing Nix stores to be shared between multiple
    machines); no recovery is needed when a Nix process crashes; no write
    access is needed for read-only operations; no more running out of Berkeley
    DB locks on certain operations.

    You still need to compile Nix with Berkeley DB support if you want Nix to
    automatically convert your old Nix store to the new schema. If you don't
    need this, you can build Nix with the configure option
    --disable-old-db-compat.

    After the automatic conversion to the new schema, you can delete the old
    Berkeley DB files:

    $ cd /nix/var/nix/db
    $ rm __db* log.* derivers references referrers reserved validpaths DB_CONFIG

    The new metadata is stored in the directories /nix/var/nix/db/info and /nix
    /var/nix/db/referrer. Though the metadata is stored in human-readable
    plain-text files, they are not intended to be human-editable, as Nix is
    rather strict about the format.

    The new storage schema may or may not require less disk space than the
    Berkeley DB environment, mostly depending on the cluster size of your file
    system. With 1 KiB clusters (which seems to be the ext3 default nowadays)
    it usually takes up much less space.

  * There is a new substituter that copies paths directly from other (remote)
    Nix stores mounted somewhere in the filesystem. For instance, you can speed
    up an installation by mounting some remote Nix store that already has the
    packages in question via NFS or sshfs. The environment variable
    NIX_OTHER_STORES specifies the locations of the remote Nix directories,
    e.g. /mnt/remote-fs/nix.

  * New nix-store operations --dump-db and --load-db to dump and reload the Nix
    database.

  * The garbage collector has a number of new options to allow only some of the
    garbage to be deleted. The option --max-freed N tells the collector to stop
    after at least N bytes have been deleted. The option --max-links N tells it
    to stop after the link count on /nix/store has dropped below N. This is
    useful for very large Nix stores on filesystems with a 32000 subdirectories
    limit (like ext3). The option --use-atime causes store paths to be deleted
    in order of ascending last access time. This allows non-recently used stuff
    to be deleted. The option --max-atime time specifies an upper limit to the
    last accessed time of paths that may be deleted. For instance,

        $ nix-store --gc -v --max-atime $(date +%s -d "2 months ago")

    deletes everything that hasn't been accessed in two months.

  * nix-env now uses optimistic profile locking when performing an operation
    like installing or upgrading, instead of setting an exclusive lock on the
    profile. This allows multiple nix-env -i / -u / -e operations on the same
    profile in parallel. If a nix-env operation sees at the end that the
    profile was changed in the meantime by another process, it will just
    restart. This is generally cheap because the build results are still in the
    Nix store.

  * The option --dry-run is now supported by nix-store -r and nix-build.

  * The information previously shown by --dry-run (i.e., which derivations will
    be built and which paths will be substituted) is now always shown by
    nix-env, nix-store -r and nix-build. The total download size of
    substitutable paths is now also shown. For instance, a build will show
    something like

    the following derivations will be built:
      /nix/store/129sbxnk5n466zg6r1qmq1xjv9zymyy7-activate-configuration.sh.drv
      /nix/store/7mzy971rdm8l566ch8hgxaf89x7lr7ik-upstart-jobs.drv
      ...
    the following paths will be downloaded/copied (30.02 MiB):
      /nix/store/4m8pvgy2dcjgppf5b4cj5l6wyshjhalj-samba-3.2.4
      /nix/store/7h1kwcj29ip8vk26rhmx6bfjraxp0g4l-libunwind-0.98.6
      ...

  * Language features:

      o @-patterns as in Haskell. For instance, in a function definition

        f = args @ {x, y, z}: ...;

        args refers to the argument as a whole, which is further
        pattern-matched against the attribute set pattern {x, y, z}.

      o "..." (ellipsis) patterns. An attribute set pattern can now say ... at
        the end of the attribute name list to specify that the function takes
        at least the listed attributes, while ignoring additional attributes.
        For instance,

        {stdenv, fetchurl, fuse, ...}: ...

        defines a function that accepts any attribute set that includes at
        least the three listed attributes.

      o New primops: builtins.parseDrvName (split a package name string like
        "nix-0.12pre12876" into its name and version components, e.g. "nix" and
        "0.12pre12876"), builtins.compareVersions (compare two version strings
        using the same algorithm that nix-env uses), builtins.length
        (efficiently compute the length of a list), builtins.mul (integer
        multiplication), builtins.div (integer division).

  * nix-prefetch-url now supports mirror:// URLs, provided that the environment
    variable NIXPKGS_ALL points at a Nixpkgs tree.

  * Removed the commands nix-pack-closure and nix-unpack-closure. You can do
    almost the same thing but much more efficiently by doing nix-store --export
    $(nix-store -qR paths) > closure and nix-store --import < closure.

  * Lots of bug fixes, including a big performance bug in the handling of
    with-expressions.

-- 
Eelco Dolstra | http://www.st.ewi.tudelft.nl/~dolstra/