perf(libstore/derivation-builder): pre-compute outputGraph for linear complexity#14540
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Ericson2314 merged 3 commits intoNixOS:masterfrom Nov 29, 2025
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OK let me know what you think @lovesegfault. The original code from @Ma27 unnecessarily made its own data structures when we already had a graph data structure on hand. If you go commit-by-commit and disable whitespace, it should be fairly easy to read.
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Nice, thanks @Ericson2314! This looks good to me :) |
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@xokdvium how is it now, with the first commit ensuring that making things by reference actually gives us value? |
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- No `std::function` overhead - Don't copy if not necessary Co-authored-by: Sergei Zimmerman <sergei@zimmerman.foo>
… complexity Build the inverse of `scratchOuputs` before running topoSort, avoiding quadratic complexity when determining which outputs reference each other. This fixes the FIXME comment about building the inverted map up front. Inspired by Lix commit 10c04ce / Change Id Ibdd46e7b2e895bfeeebc173046d1297b41998181, but ended up being completely different code. Co-Authored-By: Maximilian Bosch <maximilian@mbosch.me> Co-Authored-By: Bernardo Meurer Costa <beme@anthropic.com>
We can precompute the exact information we need for topo sorting and store it in `PerhapsNeedToRegister`. Depending on how `topoSort` works, this is easy a performance improvement or just completely harmless. Co-Authored-By: Bernardo Meurer Costa <beme@anthropic.com>
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Motivation
Build the output reference graph and inverse output map before running
topoSort, avoiding quadratic complexity when determining which outputs
reference each other. This fixes the FIXME comment about building the
inverted map up front.
The outputGraph (StorePath → StorePathSet) maps each output to its
references, and will be reused in future commits to generate detailed
cycle error messages showing which files contain problematic references.
Adapted from Lix commit 10c04ce.
Change-Id: Ibdd46e7b2e895bfeeebc173046d1297b41998181
Co-Authored-By: Maximilian Bosch maximilian@mbosch.me
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