Merge pull request #5212 from mkenigs/auto-uid-allocation

Merge master into #3600

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+# Release 0.12 (2008-11-20)
+
+  - 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:
+    
+      - @-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}`.
+    
+      - “`...`” (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.
+    
+      - 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.