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Use the hash modulo in the derivation outputs

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Rather than storing the derivation outputs as `drvPath!outputName` internally,
store them as `drvHashModulo!outputName` (or `outputHash!outputName` for
fixed-output derivations).

This makes the storage slightly more opaque, but enables an earlier
cutoff in cases where a fixed-output dependency changes (but keeps the
same output hash) − same as what we already do for input-addressed
derivations.
This commit is contained in:
regnat 2020-12-09 16:56:56 +01:00
parent 8914e01e37
commit bab1cda0e6
7 changed files with 93 additions and 89 deletions
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22
src/libstore/derivations.hh
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@ -18,8 +18,6 @@ namespace nix {
/* The traditional non-fixed-output derivation type. */
struct DerivationOutputInputAddressed
{
/* Will need to become `std::optional<StorePath>` once input-addressed
derivations are allowed to depend on cont-addressed derivations */
StorePath path;
};
@ -174,12 +172,12 @@ std::string outputPathName(std::string_view drvName, std::string_view outputName
// whose output hashes are always known since they are fixed up-front.
typedef std::map<std::string, Hash> CaOutputHashes;
struct UnknownHashes {};
struct DeferredHash { Hash hash; };
typedef std::variant<
Hash, // regular DRV normalized hash
CaOutputHashes, // Fixed-output derivation hashes
UnknownHashes // Deferred hashes for floating outputs drvs and their dependencies
DeferredHash // Deferred hashes for floating outputs drvs and their dependencies
> DrvHashModulo;
/* Returns hashes with the details of fixed-output subderivations
@ -207,22 +205,18 @@ typedef std::variant<
*/
DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutputs);
/*
Return a map associating each output to a hash that uniquely identifies its
derivation (modulo the self-references).
*/
std::map<std::string, Hash> staticOutputHashes(Store& store, const Derivation& drv);
/* Memoisation of hashDerivationModulo(). */
typedef std::map<StorePath, DrvHashModulo> DrvHashes;
// FIXME: global, though at least thread-safe.
extern Sync<DrvHashes> drvHashes;
/* Memoisation of `readDerivation(..).resove()`. */
typedef std::map<
StorePath,
std::optional<StorePath>
> DrvPathResolutions;
// FIXME: global, though at least thread-safe.
// FIXME: arguably overlaps with hashDerivationModulo memo table.
extern Sync<DrvPathResolutions> drvPathResolutions;
bool wantOutput(const string & output, const std::set<string> & wanted);
struct Source;