* `--min-age' flag in nix-store and nix-collect-garbage to only delete

  unreachable paths that haven't been used for N hours.  For instance,
  `nix-collect-garbage --min-age 168' only deletes paths that haven't
  been accessed in the last week.

  This is useful for instance in the build farm where many derivations
  can be shared between consecutive builds, and we wouldn't want a
  garbage collect to throw them all away.  We could of course register
  them as roots, but then we'd to unregister them at some point, which
  would be a pain to manage.  The `--min-age' flag gives us a sort of
  MRU caching scheme.

  BUG: this really shouldn't be in gc.cc since that violates
  mechanism/policy separation.

1 files changed, 12 insertions, 4 deletions

diff --git a/scripts/nix-collect-garbage.in b/scripts/nix-collect-garbage.in
index 539979cbb..44bcc16bb 100755
--- a/scripts/nix-collect-garbage.in
+++ b/scripts/nix-collect-garbage.in
@@ -9,16 +9,24 @@ my $storeDir = "@storedir@";
 my %alive;
 
 my $gcOper = "--delete";
-my $keepSuccessors = 1;
+my $minAge = 0;
 
 my @roots = ();
 
 
 # Parse the command line.
-foreach my $arg (@ARGV) {
+for (my $i = 0; $i < scalar @ARGV; $i++) {
+    my $arg = $ARGV[$i];
     if ($arg eq "--delete" || $arg eq "--print-live" || $arg eq "--print-dead") {
         $gcOper = $arg;
-    } else { die "unknown argument `$arg'" };
+    }
+    elsif ($arg eq "--min-age") {
+        $i++;
+        $minAge = undef;
+        $minAge = $ARGV[$i];
+        die "invalid minimum age" unless defined $minAge && $minAge =~ /^\d*$/;
+    }
+    else { die "unknown argument `$arg'" };
 }
 
 
@@ -69,7 +77,7 @@ findRoots 1, $rootsDir;
 
 
 # Run the collector with the roots we found.
-my $pid = open2(">&1", \*WRITE, "@bindir@/nix-store --gc $gcOper")
+my $pid = open2(">&1", \*WRITE, "@bindir@/nix-store --gc $gcOper --min-age $minAge")
     or die "cannot run `nix-store --gc'";
 
 foreach my $root (@roots) {