Binary caches can now specify a priority in their nix-cache-info file.
The binary cache substituter checks caches in order of priority. This
is to ensure that fast, static caches like nixos.org/binary-cache are
processed before slow, dynamic caches like hydra.nixos.org.
This allows disabling the use of binary caches, e.g.
$ nix-build ... --option use-binary-caches false
Note that
$ nix-build ... --option binary-caches ''
does not disable all binary caches, since the caches defined by
channels will still be used.
If ‘--link’ is given, nix-push will create hard links to the NAR files
in the store, rather than copying them. This is faster and requires
less disk space. However, it doesn't work if the store is on a
different file system.
I.e. do what git does. I'm too lazy to keep the builtin help text up
to date :-)
Also add ‘--help’ to various commands that lacked it
(e.g. nix-collect-garbage).
This operation allows fixing corrupted or accidentally deleted store
paths by redownloading them using substituters, if available.
Since the corrupted path cannot be replaced atomically, there is a
very small time window (one system call) during which neither the old
(corrupted) nor the new (repaired) contents are available. So
repairing should be used with some care on critical packages like
Glibc.
Commit 6a214f3e06 copied most of the Nix
shell initialisation code from NixOS to nix-profile.sh; however, that
code assumes a multi-user install and is Linux-specific (e.g. it calls
the "stat" command). So go back to the simple single-user version.
Fixes#49.
Negative lookups are purged from the DB after a day, at most once per
day. However, for non-"have" lookups (e.g. all except "nix-env
-qas"), negative lookups are ignored after one hour. This is to
ensure that you don't have to wait a day for an operation like
"nix-env -i" to start using new binaries in the cache.
Should probably make this configurable.
Note that this will only work if the client has a very recent Nix
version (post 15e1b2c223), otherwise the
--option flag will just be ignored.
Fixes#50.
This handles the chroot and build hook cases, which are easy.
Supporting the non-chroot-build case will require more work (hash
rewriting!).
Issue #21.
Output names are now appended to resulting GC symlinks, e.g. by
nix-build. For backwards compatibility, if the output is named "out",
nothing is appended. E.g. doing "nix-build -A foo" on a derivation
that produces outputs "out", "bin" and "dev" will produce symlinks
"./result", "./result-bin" and "./result-dev", respectively.
Channels can now advertise a binary cache by creating a file
<channel-url>/binary-cache-url. The channel unpacker puts these in
its "binary-caches" subdirectory. Thus, the URLS of the binary caches
for the channels added by root appear in
/nix/var/nix/profiles/per-user/eelco/channels/binary-caches/*. The
binary cache substituter reads these and adds them to the list of
binary caches.
The .nixpkg file format is extended to optionally include the URL of a
binary cache, which will be used in preference to the manifest URL
(which can be set to a non-existent value).
Querying all substitutable paths via "nix-env -qas" is potentially
hard on a server, since it involves sending thousands of HEAD
requests. So a binary cache must now have a meta-info file named
"nix-cache-info" that specifies whether the server wants this. It
also specifies the store prefix so that we don't send useless queries
to a binary cache for a different store prefix.
Since SubstitutionGoal::finished() in build.cc computes the hash
anyway, we can prevent the inefficiency of computing the hash twice by
letting the substituter tell Nix about the expected hash, which can
then verify it.
Commit 6a214f3e06 reused the NixOS
environment initialisation for nix-profile.sh, but this is
inappropriate on systems that don't have multi-user support enabled.
In "nix-env -qas", we don't need the substitute info, we just need to
know if it exists. This can be done using a HTTP HEAD request, which
saves bandwidth.
Note however that curl currently has a bug that prevents it from
reusing HTTP connections if HEAD requests return a 404:
https://sourceforge.net/tracker/?func=detail&aid=3542731&group_id=976&atid=100976
Without the patch attached to the issue, using HEAD is actually quite
a bit slower than GET.
Getting substitute information using the binary cache substituter has
non-trivial latency overhead. A package or NixOS system configuration
can have hundreds of dependencies, and in the worst case (when the
local info cache is empty) we have to do a separate HTTP request for
each of these. If the ping time to the server is t, getting N info
files will take tN seconds; e.g., with a ping time of 0.1s to
nixos.org, sequentially downloading 1000 info files (a typical NixOS
config) will take at least 100 seconds.
To fix this problem, the binary cache substituter can now perform
requests in parallel. This required changing the substituter
interface to support a function querySubstitutablePathInfos() that
queries multiple paths at the same time, and rewriting queryMissing()
to take advantage of parallelism. (Due to local caching,
parallelising queryMissing() is sufficient for most use cases, since
it's almost always called before building a derivation and thus fills
the local info cache.)
For example, parallelism speeds up querying all 1056 paths in a
particular NixOS system configuration from 116s to 2.6s. It works so
well because the eccentricity of the top-level derivation in the
dependency graph is only 9. So we only need 10 round-trips (when
using an unlimited number of parallel connections) to get everything.
Currently we do a maximum of 150 parallel connections to the server.
Thus it's important that the binary cache server (e.g. nixos.org) has
a high connection limit. Alternatively we could use HTTP pipelining,
but WWW::Curl doesn't support it and libcurl has a hard-coded limit of
5 requests per pipeline.
Using WWW::Curl rather than running an external curl process for every
NAR info file halves the time it takes to get info thanks to libcurl's
support for persistent HTTP connections. (We save a roundtrip per
file.) But the real gain will come from using parallel and/or
pipelined requests.
XZ compresses significantly better than bzip2. Here are the
compression ratios and execution times (using 4 cores in parallel) on
my /var/run/current-system (3.1 GiB):
bzip2: total compressed size 849.56 MiB, 30.8% [2m08]
xz -6: total compressed size 641.84 MiB, 23.4% [6m53]
xz -7: total compressed size 621.82 MiB, 22.6% [7m19]
xz -8: total compressed size 599.33 MiB, 21.8% [7m18]
xz -9: total compressed size 588.18 MiB, 21.4% [7m40]
Note that compression takes much longer. More importantly, however,
decompression is much faster:
bzip2: 1m47.274s
xz -6: 0m55.446s
xz -7: 0m54.119s
xz -8: 0m52.388s
xz -9: 0m51.842s
The only downside to using -9 is that decompression takes a fair
amount (~65 MB) of memory.
Manifests are a huge pain, since users need to run nix-pull directly
or indirectly to obtain them. They tend to be large and lag behind
the available binaries; also, the downloaded manifests in
/nix/var/nix/manifest need to be in sync with the Nixpkgs sources. So
we want to get rid of them.
The idea of manifest-free operation works as follows. Nix is
configured with a set of URIs of binary caches, e.g.
http://nixos.org/binary-cache
Whenever Nix needs a store path X, it checks each binary cache for the
existence of a file <CACHE-URI>/<SHA-256 hash of X>.narinfo, e.g.
http://nixos.org/binary-cache/bi1gh9...ia17.narinfo
The .narinfo file contains the necessary information about the store
path that was formerly kept in the manifest, i.e., (relative) URI of
the compressed NAR, references, size, hash, etc. For example:
StorePath: /nix/store/xqp4l88cr9bxv01jinkz861mnc9p7qfi-neon-0.29.6
URL: 1bjxbg52l32wj8ww47sw9f4qz0r8n5vs71l93lcbgk2506v3cpfd.nar.bz2
CompressedHash: sha256:1bjxbg52l32wj8ww47sw9f4qz0r8n5vs71l93lcbgk2506v3cpfd
CompressedSize: 202542
NarHash: sha256:1af26536781e6134ab84201b33408759fc59b36cc5530f57c0663f67b588e15f
NarSize: 700440
References: 043zrsanirjh8nbc5vqpjn93hhrf107f-bash-4.2-p24 cj7a81wsm1ijwwpkks3725661h3263p5-glibc-2.13 ...
Deriver: 4idz1bgi58h3pazxr3akrw4fsr6zrf3r-neon-0.29.6.drv
System: x86_64-linux
Nix then knows that it needs to download
http://nixos.org/binary-cache/1bjxbg52l32wj8ww47sw9f4qz0r8n5vs71l93lcbgk2506v3cpfd.nar.bz2
to substitute the store path.
Note that the store directory is omitted from the References and
Deriver fields to save space, and that the URL can be relative to the
binary cache prefix.
This patch just makes nix-push create binary caches in this format.
The next step is to make a substituter that supports them.
For several platforms we don't currently have "native" Nix packages
(e.g. Mac OS X and FreeBSD). This provides the next best thing: a
tarball containing the closure of Nix, plus a simple script
"nix-finish-install" that initialises the Nix database, registers the
paths in the closure as valid, and runs "nix-env -i /path/to/nix" to
initialise the user profile.
The tarball must be unpacked in the root directory. It creates
/nix/store/... and /usr/bin/nix-finish-install. Typical installation
is as follows:
$ cd /
$ tar xvf /path/to/nix-1.1pre1234_abcdef-x86_64-linux.tar.bz2
$ nix-finish-install
(if necessary add ~/.nix-profile/etc/profile.d/nix.sh to the shell
login scripts)
After this, /usr/bin/nix-finish-install can be deleted, if desired.
The downside to the binary tarball is that it's pretty big (~55 MiB
for x86_64-linux).
Mandatory features are features that MUST be present in a derivation's
requiredSystemFeatures attribute. One application is performance
testing, where we have a dedicated machine to run performance tests
(and nothing else). Then we would add the label "perf" to the
machine's mandatory features and to the performance testing
derivations.
"nix-channel --add" now accepts a second argument: the channel name.
This allows channels to have a nicer name than (say) nixpkgs_unstable.
If no name is given, it defaults to the last component of the URL
(with "-unstable" or "-stable" removed).
Also, channels are now stored in a profile
(/nix/var/nix/profiles/per-user/$USER/channels). One advantage of
this is that it allows rollbacks (e.g. if "nix-channel --update" gives
an undesirable update).
Sometimes when doing "nix-build --run-env" you don't want all
dependencies to be built. For instance, if we want to do "--run-env"
on the "build" attribute in Hydra's release.nix (to get Hydra's build
environment), we don't want its "tarball" dependency to be built. So
we can do:
$ nix-build --run-env release.nix -A build --exclude 'hydra-tarball'
This will skip the dependency whose name matches the "hydra-tarball"
regular expression. The "--exclude" option can be repeated any number
of times.
This command builds or fetches all dependencies of the given
derivation, then starts a shell with the environment variables from
the derivation. This shell also sources $stdenv/setup to initialise
the environment further.
The current directory is not changed. Thus this is a convenient way
to reproduce a build environment in an existing working tree.
Existing environment variables are left untouched (unless the
derivation overrides them). As a special hack, the original value of
$PATH is appended to the $PATH produced by $stdenv/setup.
Example session:
$ nix-build --run-env '<nixpkgs>' -A xterm
(the dependencies of xterm are built/fetched...)
$ tar xf $src
$ ./configure
$ make
$ emacs
(... hack source ...)
$ make
$ ./xterm
directory. Previously in this situation we did add the Nix
expressions from the channel to allow installation from source, but
this doesn't work for binary-only channels and leads to confusing
error messages.
