This project evaluates nix attribute sets in parallel with streamable json output. This is useful for time and memory intensive evaluations such as NixOS machines, i.e. in a CI context. The evaluation is done with a controllable number of threads that are restarted when their memory consumption exceeds a certain threshold.
To facilitate integration, nix-eval-jobs creates garbage collection roots for each evaluated derivation (drv file, not the build) within the provided attribute. This prevents race conditions between the nix garbage collection service and user-started nix builds processes.
- Faster evaluation by using threads
- Memory used for evaluation is reclaimed after nix-eval-jobs finish, so that the build can use it.
- Evaluation of jobs can fail individually
In the following example we evaluate the hydraJobs attribute of the patchelf flake:
$ nix-eval-jobs --gc-roots-dir gcroot --flake 'github:NixOS/patchelf#hydraJobs'
{"attr":"coverage","attrPath":["coverage"],"drvPath":"/nix/store/fmbqzaq8mim1423879lhn9whs6imx5w4-patchelf-coverage-0.18.0.drv","inputDrvs":{"/nix/store/23632hx2c98lbbjld279dx0w08lxn6kp-hook.drv":["out"],"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/ap9g09fxbicj836zm88d56dn3ff4clxl-stdenv-linux.drv":["out"],"/nix/store/c0gg7lj101xhd8v2b3cjl5dwwkpxfc0q-patchelf-tarball-0.18.0.drv":["out"],"/nix/store/vslywm6kbazi37q1vbq8y7bi884yc6yx-lcov-1.16.drv":["out"],"/nix/store/y964yq4vz1gsn7azd44vyg65gnr4gpvi-hook.drv":["out"]},"name":"patchelf-coverage-0.18.0","outputs":{"out":"/nix/store/gfni9sbhhwhxxfqziq1fs3n82bvw962l-patchelf-coverage-0.18.0"},"system":"x86_64-linux"}
{"attr":"patchelf-win32","attrPath":["patchelf-win32"],"drvPath":"/nix/store/s38l0fg5ja6j8qpws7slw2ws0c6v0qcf-patchelf-i686-w64-mingw32-0.18.0.drv","inputDrvs":{"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/b2p151ilwqpd47fbmzz50a5cmj12ixbf-hook.drv":["out"],"/nix/store/fbnhh18m4jh6cwa92am2sv3aqzjnzpdd-stdenv-linux.drv":["out"]},"name":"patchelf-i686-w64-mingw32-0.18.0","outputs":{"out":"/nix/store/w8r4h1xk71fryb99df8aszp83kfhw3bc-patchelf-i686-w64-mingw32-0.18.0"},"system":"x86_64-linux"}
{"attr":"patchelf-win64","attrPath":["patchelf-win64"],"drvPath":"/nix/store/wxpym6d3dxr1w9syhinp7f058gwxfmd3-patchelf-x86_64-w64-mingw32-0.18.0.drv","inputDrvs":{"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/71lv5lsr1y59bv1b91jc9gg0n85kf1sq-stdenv-linux.drv":["out"],"/nix/store/b2p151ilwqpd47fbmzz50a5cmj12ixbf-hook.drv":["out"]},"name":"patchelf-x86_64-w64-mingw32-0.18.0","outputs":{"out":"/nix/store/fkq5428l2xsb84yj0cc6q1lkvsrga7sv-patchelf-x86_64-w64-mingw32-0.18.0"},"system":"x86_64-linux"}
{"attr":"release","attrPath":["release"],"drvPath":"/nix/store/3xpwg8f623dpkh6cblv2fzcq5n99xl0j-patchelf-0.18.0.drv","inputDrvs":{"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/9rmihrl9ys0sap6827xyns0y73vqafjx-patchelf-0.18.0.drv":["out"],"/nix/store/am2zqx3pyc1i14f888jna785h0f841sg-patchelf-0.18.0.drv":["out"],"/nix/store/c0gg7lj101xhd8v2b3cjl5dwwkpxfc0q-patchelf-tarball-0.18.0.drv":["out"],"/nix/store/csjiccxbwpfv55m8kqs2xwrkkha14dnq-patchelf-0.18.0.drv":["out"],"/nix/store/jsrnpxdx5vmpnakd9bkb3sk3lgh0k8hm-patchelf-0.18.0.drv":["out"],"/nix/store/k8a51ax83554c67g98xf3y751vjgjs7m-patchelf-0.18.0.drv":["out"],"/nix/store/wq3ncl207isqqkqmsa5ql4fg19jbrhxg-stdenv-linux.drv":["out"]},"name":"patchelf-0.18.0","outputs":{"out":"/nix/store/d0mzprvv3vhasj23r1a6qn8qip0srbc4-patchelf-0.18.0"},"system":"x86_64-linux"}
{"attr":"tarball","attrPath":["tarball"],"drvPath":"/nix/store/c0gg7lj101xhd8v2b3cjl5dwwkpxfc0q-patchelf-tarball-0.18.0.drv","inputDrvs":{"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/9d754glmsvpjm5kxvgsjslvgv356kbmn-libtool-2.4.7.drv":["out"],"/nix/store/ap9g09fxbicj836zm88d56dn3ff4clxl-stdenv-linux.drv":["out"],"/nix/store/f1ksgsyplvb0sli4pls6k6vsfvmv519d-autoconf-2.71.drv":["out"],"/nix/store/jf58lcnch1bmpbi2188c59w5zr1cqrx2-automake-1.16.5.drv":["out"]},"name":"patchelf-tarball-0.18.0","outputs":{"out":"/nix/store/72pz5awc7gpwdqxrdsy8j0bvg2n7z78q-patchelf-tarball-0.18.0"},"system":"x86_64-linux"}The output here is newline-seperated json according to https://jsonlines.org.
The code is derived from hydra's eval-jobs executable.
$ nix-eval-jobs --help
USAGE: nix-eval-jobs [options] expr
--arg Pass the value *expr* as the argument *name* to Nix functions.
--argstr Pass the string *string* as the argument *name* to Nix functions.
--check-cache-status Check if the derivations are present locally or in any configured substituters (i.e. binary cache). The information will be exposed in the `cacheStatus` field of the JSON output.
--debug Set the logging verbosity level to 'debug'.
--eval-store
The [URL of the Nix store](@docroot@/command-ref/new-cli/nix3-help-stores.md#store-url-format)
to use for evaluation, i.e. to store derivations (`.drv` files) and inputs referenced by them.
--expr treat the argument as a Nix expression
--flake build a flake
--force-recurse force recursion (don't respect recurseIntoAttrs)
--gc-roots-dir garbage collector roots directory
--help show usage information
--impure allow impure expressions
--log-format Set the format of log output; one of `raw`, `internal-json`, `bar` or `bar-with-logs`.
--max-memory-size maximum evaluation memory size in megabyte (4GiB per worker by default)
--meta include derivation meta field in output
--option Set the Nix configuration setting *name* to *value* (overriding `nix.conf`).
--override-flake Override the flake registries, redirecting *original-ref* to *resolved-ref*.
--override-input Override a specific flake input (e.g. `dwarffs/nixpkgs`).
--quiet Decrease the logging verbosity level.
--repair During evaluation, rewrite missing or corrupted files in the Nix store. During building, rebuild missing or corrupted store paths.
--show-trace print out a stack trace in case of evaluation errors
--verbose Increase the logging verbosity level.
--workers number of evaluate workersFaster evaluator in deployment tools. When evaluating NixOS machines, evaluation can take several minutes when run on a single core. This limits scalability for large deployments with deployment tools such as NixOps.
Faster evaluator in CIs. In addition to evaluation speed for CIs, it is also useful if evaluation of individual jobs in CIs can fail, as opposed to failing the entire jobset. For CIs that allow dynamic build steps to be created, one can also take advantage of the fact that nix-eval-jobs outputs the derivation path separately. This allows separate logs and success status per job instead of a single large log file. In the wiki we collect example ci configuration for various CIs.
- nix-fast-build - Combine the power of nix-eval-jobs with nix-output-monitor to speed-up your evaluation and building process
- buildbot-nix - A nixos module to make buildbot a proper Nix-CI
- colmena - A simple, stateless NixOS deployment tool
- robotnix - Build Android (AOSP) using Nix, used in their CI
If you provide the --check-cache-status, the json will contain a
"cacheStatus" key in its json, with the following values:
| Value | Meaning |
|---|---|
| local | Package is present locally |
| cached | Package is present in the binary cache, but not locally |
| notBuilt | Package needs to be built. |
If you want to evaluate nixpkgs in the same way hydra does it, use this snippet:
$ nix-eval-jobs --force-recurse pkgs/top-level/release.nixBy default, nix-eval-jobs spawns as many worker processes as there are hardware threads in the system and limits the memory usage for each worker to 4GB.
However, keep in mind that each worker process may need to re-evaluate shared dependencies of the attributes, which can introduce some overhead for each evaluation or cause workers to exceed their memory limit. If you encounter these situations, you can tune the following options:
--workers: This option allows you to set the number of evaluation workers that
nix-eval-jobs should spawn. You can increase or decrease this number to optimize
the evaluation speed and memory usage. For example, if you have a system with
many CPU cores but limited memory, you may want to reduce the number of workers
to avoid exceeding the memory limit.
--max-memory-size: This option allows you to adjust the memory limit for each
worker process. By default, it's set to 4GiB, but you can increase or decrease
this value as needed. For example, if you have a system with a lot of memory and
want to speed up the evaluation, you may want to increase the memory limit to
allow workers to cache more data in memory before getting restarted by
nix-eval-jobs. Note that this is not a hard limit and memory usage may rise
above the limit momentarily before the worker process exits.
Overall, tuning these options can help you optimize the performance and memory usage of nix-eval-jobs to better fit your system and evaluation needs.