Replace fetchToStore cache by sourcePathToHash cache#14769
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Replace fetchToStore cache by sourcePathToHash cache#14769
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roberth
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Dec 11, 2025
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| // FIXME: add an optimisation for the case where the accessor is | ||
| // a `PosixSourceAccessor` pointing to a store path. |
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Don't think so, the path fetcher has an optimization that does something like that now.
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| settings.getCache()->upsert( | ||
| makeSourcePathToHashCacheKey( | ||
| *accessor->fingerprint, ContentAddressMethod::Raw::NixArchive, CanonPath::root), | ||
| {{"hash", store.queryPathInfo(storePath)->narHash.to_string(HashFormat::SRI, true)}}); |
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Suggested change
| settings.getCache()->upsert( | |
| makeSourcePathToHashCacheKey( | |
| *accessor->fingerprint, ContentAddressMethod::Raw::NixArchive, CanonPath::root), | |
| {{"hash", store.queryPathInfo(storePath)->narHash.to_string(HashFormat::SRI, true)}}); |
Tests pass without this code. It could be dead or broken.
Make sure to cover this with the _NIX_TEST_BARF_ON_UNCACHEABLE trick.
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_NIX_TEST_BARF_ON_UNCACHEABLE doesn't test that. It fails on inputs that don't have a fingerprint. If you remove the upsert, it disables caching, but there is nothing that tests that.
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I see, that is a bit different. Not a bad idea though considering how unreliable the caches have been.
(does need a different name it seems)
Ericson2314
reviewed
Feb 4, 2026
| fetchers::Cache::Key makeFetchToStoreCacheKey( | ||
| const std::string & name, const std::string & fingerprint, ContentAddressMethod method, const std::string & path) | ||
| fetchers::Cache::Key | ||
| makeSourcePathToHashCacheKey(std::string_view fingerprint, ContentAddressMethod method, const CanonPath & path) |
Ericson2314
reviewed
Feb 4, 2026
Caching NAR hashes instead of store paths makes the cache more general, because we can always compute the store path from the NAR hash, but not the other way around. This is useful for lazy trees, where we want to compute the NAR hash of an input with caching.
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Motivation
Caching NAR hashes instead of store paths makes the cache more general, because we can always compute the store path from the NAR hash, but not the other way around. This is useful for lazy trees, where we want to compute the NAR hash of an input with caching.
This PR also cherry-picks DeterminateSystems#157, which adds a
Store::maybeQueryPathInfo()method. This is preferred overisValidPath()because it has better caching.Context
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