This speeds up commands like "nix cat-store". For example:
$ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nar-cache /nix/store/i60yncmq6w9dyv37zd2k454g0fkl3arl-systemd-234/etc/udev/udev.conf
real 0m4.336s
$ time nix cat-store --store https://cache.nixos.org?local-nar-cache=/tmp/nar-cache /nix/store/i60yncmq6w9dyv37zd2k454g0fkl3arl-systemd-234/etc/udev/udev.conf
real 0m0.045s
The primary motivation is to allow hydra-server to serve files from S3
binary caches. Previously Hydra had a hack to do "nix-store -r
<path>", but that fetches the entire closure so is prohibitively
expensive.
There is no garbage collection of the NAR cache yet. Also, the entire
NAR is read when accessing a single member file. We could generate the
NAR listing to provide random access.
Note: the NAR cache is indexed by the store path hash, not the content
hash, so NAR caches should not be shared between binary caches, unless
you're sure that all your builds are binary-reproducible.
Probably as a result of a bad merge in
4b8f1b0ec0, we had both a
BinaryCacheStoreAccessor and a
RemoteFSAccessor. BinaryCacheStore::getFSAccessor() returned the
latter, but BinaryCacheStore::addToStore() checked for the
former. This probably caused hydra-queue-runner to download paths that
it just uploaded.
This check spuriously fails for e.g. git@github.com:NixOS/nixpkgs.git,
and even for ssh://git@github.com/NixOS/nixpkgs.git, and is made
redundant by the checks git itself will do when fetching the repo. We
instead pass a -- before passing the URI to git to avoid injection.
I needed this to test ACL/xattr removal in
canonicalisePathMetaData(). Might also be useful if you need to build
old Nixpkgs that doesn't have the required patches to remove
setuid/setgid creation.
The worker threads could exit prematurely if they finished processing
all items while the main thread was still adding items. In particular,
this caused hanging nix-store --serve processes in the build farm.
Also, process items from the main thread.
It was getting too much like whac-a-mole listing all the retriable error
conditions, so we now retry by default and list the cases where retrying
is almost certainly hopeless.
I find the error message 'nix-env --set-flag priority NUMBER PKGNAME'
not as helpful as it could be :
- doesn't share the current priorities
- doesn't say that the command must be run on the already installed
PKGNAME (which is confusing the first time)
- the doc needs careful reading:
"If there are multiple derivations matching a name in args that have the same name (e.g., gcc-3.3.6 and gcc-4.1.1), then the derivation with the highest priority is used."
if one stops reading there, he is screwed. Salvation comes with reading "A derivation can define a priority by declaring the meta.priority attribute. This attribute should be a number, with a higher value denoting a lower priority. The default priority is 0."
To sum it up, lower number wins. I tried to convey this idea in the
message too.
This is a hack to make hydra-queue-runner free its temproots
periodically, thereby ensuring that garbage collection of the
corresponding paths is not blocked until the queue runner is
restarted.
It would be better if temproots could be released earlier than at
process exit. I started working on a RAII object returned by functions
like addToStore() that releases temproots. However, this would be a
pretty massive change so I gave up on it for now.
For example,
$ nix-store -q --roots /nix/store/7phd2sav7068nivgvmj2vpm3v47fd27l-patchelf-0.8pre845_0315148
{temp:1}
denotes that the path is only being kept alive by a temporary root
(i.e. /nix/var/nix/temproots/). Similarly,
$ nix-store --gc --print-roots
...
{memory:9} -> /nix/store/094gpjn9f15ip17wzxhma4r51nvsj17p-curl-7.53.1
shows that curl is being used by some process.
This command shows why a package has another package in its runtime
closure. For example, to see why VLC has libdrm.dev in its closure:
$ nix why-depends nixpkgs.vlc nixpkgs.libdrm.dev
/nix/store/g901z9pcj0n5yy5n6ykxk3qm4ina1d6z-vlc-2.2.5.1:
lib/libvlccore.so.8.0.0: …nfig:/nix/store/405lmx6jl8lp0ad1vrr6j498chrqhz8g-libdrm-2.4.75-d…
/nix/store/s3nm7kd8hlcg0facn2q1ff2n7wrwdi2l-mesa-noglu-17.0.7-dev:
nix-support/propagated-native-build-inputs: …-dev /nix/store/405lmx6jl8lp0ad1vrr6j498chrqhz8g-libdrm-2.4.75-d…
Thus, VLC's lib/libvlccore.so.8.0.0 as well as mesa-noglu's
nix-support/propagated-native-build-inputs cause the dependency.
In particular, process() won't return as long as there are active
items. This prevents work item lambdas from referring to stack frames
that no longer exist.
Since we may use a dedicated file descriptor in the future, this
allows us to change it. So builders can do
if [[ -n $NIX_LOG_FD ]]; then
echo "@nix { message... }" >&$NIX_LOG_FD
fi
Nix can now automatically run the garbage collector during builds or
while adding paths to the store. The option "min-free = <bytes>"
specifies that Nix should run the garbage collector whenever free
space in the Nix store drops below <bytes>. It will then delete
garbage until "max-free" bytes are available.
Garbage collection during builds is asynchronous; running builds are
not paused and new builds are not blocked. However, there also is a
synchronous GC run prior to the first build/substitution.
Currently, no old GC roots are deleted (as in "nix-collect-garbage
-d").
Since file locks are per-process rather than per-file-descriptor, the
garbage collector would always acquire a lock on its own temproots
file and conclude that it's stale.
