"No space left on device" instead of "Success").  Reported by Karina
  Olmos.

  useful way to transfer the closure of a store path to another
  machine.

  These commands provide functionality previously possible through
  `nix-push --copy'.  However, they are much more convenient in many
  situations (though possibly less efficient).
  
  Example:
  $ nix-pack-closure /nix/store/hj232g1r...-subversion-1.3.0 > svn.closure
  (on another machine:)
  $ nix-unpack-closure < svn.closure

  Note that Subversion is added to the store, but not installed into a
  user environment.  One should do `nix-env -i
  /nix/store/hj232g1r...-subversion-1.3.0' for that.

  Another example: copy the application Azureus to the machine
  `scratchy' through ssh:
  
  $ nix-pack-closure $(which azureus) | ssh scratchy nix-unpack-closure

  build directory (TMPDIR, i.e., /tmp).  Fixes NIX-26.

  deletes a path even if it is reachable from a root.  However, it
  won't delete a path that still has referrers (since that would
  violate store invariants).

  Don't try this at home.  It's a useful hack for recovering from
  certain situations in a somewhat clean way (e.g., holes in closures
  due to disk corruption).

  specified paths from the Nix store.  However, this operation is
  safe: it refuses to delete anything that the garbage collector
  wouldn't delete.

  (even when it is interrupted by a signal).

  Berkeley DB from running out of locks.

  nix-store query options `--referer' and `--referer-closure' have
  been changed to `--referrer' and `--referrer-closure' (but the old
  ones are still accepted for compatibility).

  mapping.  The referer table is replaced by a referrer table (note
  spelling fix) that stores each referrer separately.  That is,
  instead of having

    referer[P] = {Q_1, Q_2, Q_3, ...}

  we store

    referer[(P, Q_1)] = ""
    referer[(P, Q_2)] = ""
    referer[(P, Q_3)] = ""
    ...

  To find the referrers of P, we enumerate over the keys with a value
  lexicographically greater than P.  This requires the referrer table
  to be stored as a B-Tree rather than a hash table.

  (The tuples (P, Q) are stored as P + null-byte + Q.)

  Old Nix databases are upgraded automatically to the new schema.

  (de)registration, in particular garbage collection (NIX-23).

  crashed Nix instances, and toss out our own recovery code.

* Checkpoint after an upgrade.

  much faster.

  Nix is properly shut down when it receives those signals.  In
  particular this ensures that killing the garbage collector doesn't
  cause a subsequent database recovery.

  result of parsing) can have very heavy sharing, causing exponential
  complexity if we naively recurse into them.  ATerms are graphs, not
  trees!

  simultaneously.  We do this using exclusive locks on uid files in
  /nix/var/nix/userpool, e.g., /nix/var/nix/userpool/123 for uid 123.