* Release notes.
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Eelco Dolstra
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1 changed files with 138 additions and 18 deletions
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@ -12,26 +12,85 @@
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<itemizedlist>
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<listitem><para>TODO: Berkeley DB no longer needed.</para></listitem>
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<listitem>
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<para>Nix no longer uses Berkeley DB to store Nix store metadata.
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The principal advantages of the new storage scheme are: it works
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properly over decent implementations of NFS (allowing Nix stores
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to be shared between multiple machines); no recovery is needed
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when a Nix process crashes; no write access is needed for
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read-only operations; no more running out of Berkeley DB locks on
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certain operations.</para>
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<listitem><para>New substituter to copy from remotely mounted Nix
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stores (TODO: document).</para></listitem>
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<para>You still need to compile Nix with Berkeley DB support if
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you want Nix to automatically convert your old Nix store to the
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new schema. If you don’t need this, you can build Nix with the
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<filename>configure</filename> option
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<option>--disable-old-db-compat</option>.</para>
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<listitem><para><command>nix-store --dump-db / --load-db</command>.</para></listitem>
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<para>After the automatic conversion to the new schema, you can
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delete the old Berkeley DB files:
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<listitem><para>New primops:
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<varname>builtins.parseDrvName</varname>,
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<varname>builtins.compareVersions</varname>,
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<varname>builtins.length</varname>,
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<varname>builtins.add</varname>,
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<varname>builtins.sub</varname>,
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<varname>builtins.genericClosure</varname>.
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</para></listitem>
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<screen>
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$ cd /nix/var/nix/db
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$ rm __db* log.* derivers references referrers reserved validpaths DB_CONFIG</screen>
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<listitem><para>GC options: <option>--max-freed</option>,
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<option>--max-links</option>.</para></listitem>
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The new metadata is stored in the directories
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<filename>/nix/var/nix/db/info</filename> and
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<filename>/nix/var/nix/db/referrer</filename>. Though the
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metadata is stored in human-readable plain-text files, they are
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not intended to be human-editable, as Nix is rather strict about
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the format.</para>
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<listitem><para>TODO: Optimistic profile locking.</para></listitem>
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<para>The new storage schema may or may not require less disk
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space than the Berkeley DB environment, mostly depending on the
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cluster size of your file system. With 1 KiB clusters (which
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seems to be the <literal>ext3</literal> default nowadays) it
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usually takes up much less space.</para>
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</listitem>
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<listitem><para>There is a new substituter that copies paths
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directly from other (remote) Nix stores mounted somewhere in the
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filesystem. For instance, you can speed up an installation by
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mounting some remote Nix store that already has the packages in
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question via NFS or <literal>sshfs</literal>. The environment
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variable <envar>NIX_OTHER_STORES</envar> specifies the locations of
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the remote Nix directories,
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e.g. <literal>/mnt/remote-fs/nix</literal>.</para></listitem>
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<listitem><para>New <command>nix-store</command> operations
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<option>--dump-db</option> and <option>--load-db</option> to dump
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and reload the Nix database.</para></listitem>
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<listitem><para>The garbage collector has a number of new options to
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allow only some of the garbage to be deleted. The option
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<option>--max-freed <replaceable>N</replaceable></option> tells the
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collector to stop after at least <replaceable>N</replaceable> bytes
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have been deleted. The option <option>--max-links
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<replaceable>N</replaceable></option> tells it to stop after the
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link count on <filename>/nix/store</filename> has dropped below
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<replaceable>N</replaceable>. This is useful on very large Nix
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stores on filesystems with a 32000 subdirectories limit (like
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<literal>ext3</literal>). The option <option>--use-atime</option>
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causes store paths to be deleted in order of ascending last access
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time. This allows non-recently used stuff to be deleted. The
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option <option>--max-atime <replaceable>time</replaceable></option>
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specifies an upper limit to the last accessed time of paths that may
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be deleted. For instance,
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<screen>
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$ nix-store --gc -v --max-atime $(date +%s -d "2 months ago")</screen>
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deletes everything that hasn’t been accessed in two months.</para></listitem>
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<listitem><para><command>nix-env</command> now uses optimistic
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profile locking when performing an operation like installing or
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upgrading, instead of setting an exclusive lock on the profile.
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This allows multiple <command>nix-env -i / -u / -e</command>
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operations on the same profile in parallel. If a
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<command>nix-env</command> operation sees at th end that the profile
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was changed in the meantime by another process, it will just
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restart. This is generally cheap because the build results are
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still in the Nix store.</para></listitem>
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<listitem><para>The option <option>--dry-run</option> is now
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supported by <command>nix-store -r</command> and
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@ -42,17 +101,78 @@
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and which paths will be substituted) is now always shown by
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<command>nix-env</command>, <command>nix-store -r</command> and
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<command>nix-build</command>. The total download size of
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substitutable paths is now also shown.</para></listitem>
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substitutable paths is now also shown. For instance, a build will
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show something like
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<screen>
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the following derivations will be built:
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/nix/store/129sbxnk5n466zg6r1qmq1xjv9zymyy7-activate-configuration.sh.drv
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/nix/store/7mzy971rdm8l566ch8hgxaf89x7lr7ik-upstart-jobs.drv
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...
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the following paths will be downloaded/copied (30.02 MiB):
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/nix/store/4m8pvgy2dcjgppf5b4cj5l6wyshjhalj-samba-3.2.4
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/nix/store/7h1kwcj29ip8vk26rhmx6bfjraxp0g4l-libunwind-0.98.6
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...</screen>
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</para></listitem>
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<listitem><para>Language features:
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<itemizedlist>
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<listitem><para>@-patterns as in Haskell. For instance, in a
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function definition
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<programlisting>f = args @ {x, y, z}: <replaceable>...</replaceable>;</programlisting>
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<varname>args</varname> refers to the argument as a whole, which
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is further pattern-matched against the attribute set pattern
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<literal>{x, y, z}</literal>.</para></listitem>
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<listitem><para>“<literal>...</literal>” (ellipsis) patterns.
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An attribute set pattern can now say <literal>...</literal> at
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the end of the attribute name list to specify that the function
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takes <emphasis>at least</emphasis> the listed attributes, while
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ignoring additional attributes. For instance,
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<programlisting>{stdenv, fetchurl, fuse, ...}: <replaceable>...</replaceable></programlisting>
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defines a function that accepts any attribute set that includes
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at least the three listed attributes.</para></listitem>
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<listitem><para>New primops:
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<varname>builtins.parseDrvName</varname> (split a package name
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string like <literal>"nix-0.12pre12876"</literal> into its name
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and version components, e.g. <literal>"nix"</literal> and
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<literal>"0.12pre12876"</literal>),
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<varname>builtins.compareVersions</varname> (compare two version
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strings using the same algorithm that <command>nix-env</command>
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uses), <varname>builtins.length</varname> (efficiently compute
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the length of a list), <varname>builtins.mul</varname> (integer
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multiplication), <varname>builtins.div</varname> (integer
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division).
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<!-- <varname>builtins.genericClosure</varname> -->
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</para></listitem>
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</itemizedlist>
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</para></listitem>
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<listitem><para><command>nix-prefetch-url</command> now supports
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<literal>mirror://</literal> URLs.</para></listitem>
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<literal>mirror://</literal> URLs, provided that the environment
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variable <envar>NIXPKGS_ALL</envar> points at a Nixpkgs
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tree.</para></listitem>
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<listitem><para>Removed the commands
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<command>nix-pack-closure</command> and
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<command>nix-unpack-closure</command>. You can do almost the same
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thing but much more efficiently by doing <literal>nix-store --export
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$(nix-store -qR <replaceable>paths</replaceable>) > closure</literal> and
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<literal>nix-store --import < closure</literal>.</para></listitem>
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<literal>nix-store --import <
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closure</literal>.</para></listitem>
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<listitem><para>Lots of bugfixes, including a big performance bug in
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the handling of <literal>with</literal>-expressions.</para></listitem>
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</itemizedlist>
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