create cache entry for paths already in the nix store#12911
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roberth merged 1 commit intoNixOS:masterfrom Apr 4, 2025
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create cache entry for paths already in the nix store#12911roberth merged 1 commit intoNixOS:masterfrom
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This looks like an ok fix in terms of behavior, but I'm a little worried about the duplication between getAccessor and fetchToStore. Presumably the former could use the latter, or a factored out method?
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I am not quite sure how this is supposed to work. But I would also suggest that we would have a simple way to fix this issue because this is something I also want to backport. |
This allows path:/nix/store/* paths to not be copied twice to the nix store.
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…2911 create cache entry for paths already in the nix store (backport #12911)
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…2911 create cache entry for paths already in the nix store (backport #12911)
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…2911 create cache entry for paths already in the nix store (backport #12911)
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…2911 create cache entry for paths already in the nix store (backport #12911)
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Part of releases:
2.28 is a continuation of 2.27. |
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This pull request has been mentioned on NixOS Discourse. There might be relevant details there: https://discourse.nixos.org/t/2025-04-09-clan-weekly-changelog/62846/1 |
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This pull request has been mentioned on NixOS Discourse. There might be relevant details there: https://discourse.nixos.org/t/nix-copying-a-store-path-into-the-store/60409/16 |
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Previously when creating the accessor for substituted/cached inputs, Nix would neither: - Ensure a cache entry exists for the substituted inputs (which are already in the store) - Use the cache for substituted inputs. Instead, it attempted to find the always missing fingerprint of the original, unsubstituted input Both of these led to severe slowdowns in some scenarios where a large input (like Nixpkgs) had already been unpacked to the store but didn't exist in a users cache, as described in NixOS#11228 The work in NixOS#12911 already fixed this in most cases, but here we can ensure it applies to the substituted store paths used for inputs
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Previously when creating the accessor for substituted/cached inputs, Nix would neither: - Ensure a cache entry exists for the substituted inputs (which are already in the store) - Use the cache for substituted inputs. Instead, it attempted to find the always missing fingerprint of the original, unsubstituted input Both of these led to severe slowdowns in some scenarios where a large input (like Nixpkgs) had already been unpacked to the store but didn't exist in a users cache, as described in NixOS#11228 The work in NixOS#12911 already fixed this in most cases, but here we can ensure it applies to the substituted store paths used for inputs
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Previously, Nix would not create a cache entry for substituted/cached inputs This led to severe slowdowns in some scenarios where a large input (like Nixpkgs) had already been unpacked to the store but didn't exist in a users cache, as described in NixOS#11228 Using the same method as NixOS#12911, we can create a cache entry for the fingerprint of substituted/cached inputs and avoid this problem entirely
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Previously, Nix would not create a cache entry for substituted/cached inputs This led to severe slowdowns in some scenarios where a large input (like Nixpkgs) had already been unpacked to the store but didn't exist in a users cache, as described in NixOS#11228 Using the same method as NixOS#12911, we can create a cache entry for the fingerprint of substituted/cached inputs and avoid this problem entirely
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This allows path:/nix/store/* paths to not be copied twice to the nix store.
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