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Excessive amount of .drv GC roots will slow significantly any GC operation #930

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opened 2025-07-25 23:38:42 +00:00 by raito · 0 comments
raito commented 2025-07-25 23:38:42 +00:00
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Is your feature request related to a problem? Please describe.

Evaluate a couple of Nixpkgs and place GC roots for every of their .drv.

(Let's say: have 600-800K GC roots.)

Run any GC operation, strace it, notice that it's spending its whole life readlinking from the auto GC root and stumbling on your active GC roots for these .drv.

Describe the solution you'd like

GC performance should not be THAT affected.

Describe alternatives you've considered

Do not be like Raito, do not evaluate a couple of nixpkgs.

Additional context

This came up because I have development trees of software that performs a lot of evaluation (evolive & security tracker).

## Is your feature request related to a problem? Please describe. Evaluate a couple of Nixpkgs and place GC roots for every of their .drv. (Let's say: have 600-800K GC roots.) Run any GC operation, strace it, notice that it's spending its whole life readlinking from the auto GC root and stumbling on your active GC roots for these .drv. ## Describe the solution you'd like GC performance should not be *THAT* affected. ## Describe alternatives you've considered Do not be like Raito, do not evaluate a couple of nixpkgs. ## Additional context This came up because I have development trees of software that performs a lot of evaluation (evolive & security tracker).
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Affects/CppNix

Probably affects CppNix. This is a best-effort tag for troubles in old code; it exists to inform the CppNix team about problems they might care about also.

  
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Found in Lix nightly.

  
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Tag for regressions in Lix nightly. We intend to fix all of these prior to releases.

  
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Affects the stable release of Lix. Usually such issues affect nightly too but there is no guarantee.

  
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language design, features, extensions, etc

  
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nix-eval-jobs for Lix

  
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profiles: nix-env, nix profile, and installer flavors all alike

  
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crash 💥

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regarding an external tool's usage with Lix (e.g. nix-eval-jobs)

  
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bug is relatively simple and could simply be fixed with some minor effort

  
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this issue should probably be solved with close involvement of an expert

  
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maintainers may not get to this soon, but we want it fixed

  
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This bug is reproducible and obvious.

  
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this bug cannot be fixed properly without fixing a known architectural flaw

  
imported

Issue imported from upstream nix (please do not remove this label, it will cause dupes if import is rerun)

  
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Affects specifically Lix on Linux

  
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performance

make lix go faster

  
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We chose not to change this (see issue comments for more detail).

  
testing

Tests that should be added

  
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Tests that are unreliable/flakey (not to be confused with flakes that test)

  
Topic/Large Scale Installations

Large scale installations of Lix, e.g. NixOS Hydra, Lix CI, big corporate installations etc.

  
ux

makes the user experience better :)

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Reference: lix-project/lix#930
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