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| author | Ludovic Courtès <ludo@gnu.org> | 2015-07-22 18:35:43 +0200 |
|---|---|---|
| committer | Ludovic Courtès <ludo@gnu.org> | 2015-07-22 22:56:41 +0200 |
| commit | 1eabf4ec63587a90fd8ea05a07f832d240dc3967 (patch) | |
| tree | d8d16b9a0fb251a1769f16a0c4214d703512679b | |
| parent | b59df2434aafb8604df38662be1b428bd19b80d6 (diff) | |
| download | gnu-guix-1eabf4ec63587a90fd8ea05a07f832d240dc3967.tar gnu-guix-1eabf4ec63587a90fd8ea05a07f832d240dc3967.tar.gz | |
derivations: Improve docstring of 'substitution-oracle'.
* guix/derivations.scm (substitution-oracle): Improve docstring.
| -rw-r--r-- | guix/derivations.scm | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/guix/derivations.scm b/guix/derivations.scm index d694ccf6d4..342a6c83f3 100644 --- a/guix/derivations.scm +++ b/guix/derivations.scm @@ -242,8 +242,10 @@ result is the set of prerequisites of DRV not already in valid." (define* (substitution-oracle store drv) "Return a one-argument procedure that, when passed a store file name, returns #t if it's substitutable and #f otherwise. The returned procedure -knows about all substitutes for all the derivations listed in DRV; it also -knows about their prerequisites, unless they are themselves substitutable. +knows about all substitutes for all the derivations listed in DRV, *except* +those that are already valid (that is, it won't bother checking whether an +item is substitutable if it's already on disk); it also knows about their +prerequisites, unless they are themselves substitutable. Creating a single oracle (thus making a single 'substitutable-paths' call) and reusing it is much more efficient than calling 'has-substitutes?' or similar |