lix/src/libexpr/flake/eval-cache.hh
Eelco Dolstra 6644b6099b
Add flake evaluation cache
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.
2019-06-07 22:25:48 +02:00

40 lines
654 B
C++

#pragma once
#include "sync.hh"
#include "flake.hh"
namespace nix { struct SQLite; struct SQLiteStmt; }
namespace nix::flake {
class EvalCache
{
struct State;
std::unique_ptr<Sync<State>> _state;
EvalCache();
public:
struct Derivation
{
Path drvPath;
Path outPath;
std::string outputName;
};
void addDerivation(
const Fingerprint & fingerprint,
const std::string & attrPath,
const Derivation & drv);
std::optional<Derivation> getDerivation(
const Fingerprint & fingerprint,
const std::string & attrPath);
static EvalCache & singleton();
};
}