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This command fetches all inputs of a flake in parallel. Example runtime for $ chmod -R u+w /tmp/nix2; rm -rf /tmp/nix2; rm ~/.cache/nix/fetcher-cache-v3.sqlite*; rm -rf ~/.cache/nix/tarball-cache/ ~/.cache/nix/gitv3/; time nix flake prefetch-inputs --store /tmp/nix2 https://api.flakehub.com/f/pinned/informalsystems/cosmos.nix/0.3.0/018ce9ed-d0be-7ce5-81b6-a3c6e3ae1187/source.tar.gz with http-connections = 1: real 4m11.859s user 2m6.931s sys 0m25.619s and http-connections = 25 (the default): real 0m57.146s user 2m49.506s sys 0m36.008s
roberth
reviewed
Jul 30, 2025
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| auto flake = lockFlake(); | ||
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| ThreadPool pool{fileTransferSettings.httpConnections}; |
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Using http-connections is weird if your inputs aren't all tarballs.
Looks like the setting needs to be generalized, or we should apply a different strategy.
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It's not perfect, but I didn't want to add another setting just for this command. http-connections is the closest to want we want to express here (i.e. an operation that is network-bound).
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Team discussion:
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roberth
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Aug 20, 2025
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This pull request has been mentioned on NixOS Discourse. There might be relevant details there: https://discourse.nixos.org/t/2025-08-20-nix-team-meeting-minutes-242-241/68245/1 |
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This pull request has been mentioned on NixOS Discourse. There might be relevant details there: |
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Motivation
This command fetches all inputs of a flake in parallel. This can be a lot faster than the serialized on-demand fetching during regular flake evaluation. The downside is that it may fetch inputs that aren't normally used.
Example runtime for
with
http-connections = 1:and
http-connections = 25(the default):Based on DeterminateSystems#127.
Context
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