diff options
| -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 |