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6644b6099b
This exploits the hermetic nature of flake evaluation to speed up
repeated evaluations of a flake output attribute.
For example (doing 'nix build' on an already present package):
$ time nix build nixpkgs:firefox
real 0m1.497s
user 0m1.160s
sys 0m0.139s
$ time nix build nixpkgs:firefox
real 0m0.052s
user 0m0.038s
sys 0m0.007s
The cache is ~/.cache/nix/eval-cache-v1.sqlite, which has entries like
INSERT INTO Attributes VALUES(
X'92a907d4efe933af2a46959b082cdff176aa5bfeb47a98fabd234809a67ab195',
'packages.firefox',
1,
'/nix/store/pbalzf8x19hckr8cwdv62rd6g0lqgc38-firefox-67.0.drv /nix/store/g6q0gx0v6xvdnizp8lrcw7c4gdkzana0-firefox-67.0 out');
where the hash 92a9... is a fingerprint over the flake store path and
the contents of the lockfile. Because flakes are evaluated in pure
mode, this uniquely identifies the evaluation result.
40 lines
654 B
C++
40 lines
654 B
C++
#pragma once
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#include "sync.hh"
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#include "flake.hh"
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namespace nix { struct SQLite; struct SQLiteStmt; }
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namespace nix::flake {
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class EvalCache
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{
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struct State;
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std::unique_ptr<Sync<State>> _state;
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EvalCache();
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public:
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struct Derivation
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{
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Path drvPath;
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Path outPath;
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std::string outputName;
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};
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void addDerivation(
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const Fingerprint & fingerprint,
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const std::string & attrPath,
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const Derivation & drv);
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std::optional<Derivation> getDerivation(
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const Fingerprint & fingerprint,
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const std::string & attrPath);
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static EvalCache & singleton();
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};
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}
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