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fetchToStore(): Avoid duplicate copying if the input is already a store path #10511

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fetchToStore(): Avoid duplicate copying if the input is already a store path #10511

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fetchToStore(): Avoid duplicate copying if the input is already a sto…
edolstra Apr 15, 2024
295cd2d
Merge remote-tracking branch 'origin/master' into optimize-fetchToStore
edolstra May 8, 2024
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13 changes: 11 additions & 2 deletions src/libfetchers/fetch-to-store.cc
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
#include "fetch-to-store.hh"
#include "fetchers.hh"
#include "cache.hh"
#include "posix-source-accessor.hh"

namespace nix {

Expand All @@ -13,8 +14,16 @@ StorePath fetchToStore(
PathFilter * filter,
RepairFlag repair)
{
// FIXME: add an optimisation for the case where the accessor is
// a `PosixSourceAccessor` pointing to a store path.
if (path.accessor->isStorePath
&& path.path.isRoot()
&& method == FileIngestionMethod::Recursive
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What goes wrong if we skip this? I am trying to special-case NAR hashing less in Nix currently.

Suggested change
&& method == FileIngestionMethod::Recursive

&& !filter)
{
if (auto accessor = path.accessor.dynamic_pointer_cast<PosixSourceAccessor>())
if (auto storePath = store.maybeParseStorePath(accessor->root.string()))
if (storePath->name() == name)
return *storePath;
}

std::optional<fetchers::Cache::Key> cacheKey;

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7 changes: 6 additions & 1 deletion src/libfetchers/path.cc
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Expand Up @@ -155,7 +155,12 @@ struct PathInputScheme : InputScheme
}
input.attrs.insert_or_assign("lastModified", uint64_t(mtime));

return {makeStorePathAccessor(store, *storePath), std::move(input)};
auto accessor = makeStorePathAccessor(store, *storePath);

/* Optimize fetchToStore() calls on this path. */
accessor->isStorePath = true;

return {accessor, std::move(input)};
}

std::optional<std::string> getFingerprint(ref<Store> store, const Input & input) const override
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3 changes: 3 additions & 0 deletions src/libfetchers/unix/mercurial.cc
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Expand Up @@ -339,6 +339,9 @@ struct MercurialInputScheme : InputScheme

accessor->setPathDisplay("«" + input.to_string() + "»");

/* Optimize fetchToStore() calls on this path. */
accessor->isStorePath = true;

return {accessor, input};
}

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7 changes: 7 additions & 0 deletions src/libutil/source-accessor.hh
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Expand Up @@ -181,6 +181,13 @@ struct SourceAccessor : std::enable_shared_from_this<SourceAccessor>
*/
virtual std::optional<time_t> getLastModified()
{ return std::nullopt; }

/**
* Whether this is a store path using
* FileIngestionMethod::Recursive. This is used to optimize
* `fetchToStore()`.
*/
bool isStorePath = false;
};

/**
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