diff --git a/doc/dev-notes.txt b/doc/dev-notes.txt
index 47274125..54fb7c3a 100644
--- a/doc/dev-notes.txt
+++ b/doc/dev-notes.txt
@@ -167,3 +167,8 @@
 * Find the builds with the highest number of build steps:
 
   select id, (select count(*) from buildsteps where build = x.id) as n from builds x order by n desc;
+
+
+* Evaluating the NixOS Hydra jobs:
+
+  $ ./hydra_eval_jobs ~/Dev/nixos-wc/release.nix --arg nixpkgs '{outPath = /home/eelco/Dev/nixpkgs-wc;}' --arg nixosSrc '{outPath = /home/eelco/Dev/nixos-wc; rev = 1234;}' --arg services '{outhPath = /home/eelco/services-wc;}' --argstr system i686-linux --argstr system x86_64-linux --arg officialRelease false
diff --git a/src/c/hydra_eval_jobs.cc b/src/c/hydra_eval_jobs.cc
index 2b09b5be..79b2ce95 100644
--- a/src/c/hydra_eval_jobs.cc
+++ b/src/c/hydra_eval_jobs.cc
@@ -21,8 +21,9 @@ void printHelp()
 static Path gcRootsDir;
 
 
-typedef std::map<Symbol, std::pair<unsigned int, Value> > ArgsUsed;
-typedef std::map<Symbol, list<Value> > AutoArgs;
+typedef std::map<Symbol, std::pair<unsigned int, Value *> > ArgsUsed;
+typedef std::list<Value *, traceable_allocator<Value *> > ValueList;
+typedef std::map<Symbol, ValueList> AutoArgs;
 
 
 static void findJobs(EvalState & state, XMLWriter & doc,
@@ -38,10 +39,10 @@ static void tryJobAlts(EvalState & state, XMLWriter & doc,
     const Bindings & actualArgs)
 {
     if (cur == last) {
-        Value v, arg;
-        state.mkAttrs(arg);
-        *arg.attrs = actualArgs;
-        mkApp(v, fun, arg);
+        Value v, * arg = state.allocValue();
+        state.mkAttrs(*arg, 0);
+        *arg->attrs = actualArgs;
+        mkApp(v, fun, *arg);
         findJobs(state, doc, argsUsed, argsLeft, v, attrPath);
         return;
     }
@@ -55,12 +56,13 @@ static void tryJobAlts(EvalState & state, XMLWriter & doc,
     Formals::Formals_::iterator next = cur; ++next;
 
     int n = 0;
-    foreach (list<Value>::const_iterator, i,  a->second) {
+    foreach (ValueList::const_iterator, i, a->second) {
         Bindings actualArgs2(actualArgs); // !!! inefficient
         ArgsUsed argsUsed2(argsUsed);
         AutoArgs argsLeft2(argsLeft);
-        actualArgs2[cur->name].value = *i;
-        argsUsed2[cur->name] = std::pair<unsigned int, Value>(n, *i);
+        actualArgs2.push_back(Attr(cur->name, *i));
+        actualArgs2.sort(); // !!! inefficient
+        argsUsed2[cur->name] = std::pair<unsigned int, Value *>(n, *i);
         argsLeft2.erase(cur->name);
         tryJobAlts(state, doc, argsUsed2, argsLeft2, attrPath, fun, next, last, actualArgs2);
         ++n;
@@ -73,7 +75,7 @@ static void showArgsUsed(XMLWriter & doc, const ArgsUsed & argsUsed)
     foreach (ArgsUsed::const_iterator, i, argsUsed) {
         XMLAttrs xmlAttrs2;
         xmlAttrs2["name"] = i->first;
-        xmlAttrs2["value"] = (format("%1%") % i->second.second).str();
+        xmlAttrs2["value"] = (format("%1%") % *i->second.second).str();
         xmlAttrs2["altnr"] = int2String(i->second.first);
         doc.writeEmptyElement("arg", xmlAttrs2);
     }
@@ -105,7 +107,7 @@ static void findJobsWrapped(EvalState & state, XMLWriter & doc,
     Value & v, const string & attrPath)
 {
     debug(format("at path `%1%'") % attrPath);
-    
+
     state.forceValue(v);
 
     if (v.type == tAttrs) {
@@ -162,8 +164,8 @@ static void findJobsWrapped(EvalState & state, XMLWriter & doc,
 
         else {
             foreach (Bindings::iterator, i, *v.attrs)
-                findJobs(state, doc, argsUsed, argsLeft, i->second.value,
-                    (attrPath.empty() ? "" : attrPath + ".") + (string) i->first);
+                findJobs(state, doc, argsUsed, argsLeft, *i->value,
+                    (attrPath.empty() ? "" : attrPath + ".") + (string) i->name);
         }
     }
 
@@ -212,11 +214,11 @@ void run(Strings args)
             string name = *i++;
             if (i == args.end()) throw UsageError("missing argument");
             string value = *i++;
-            Value v;
+            Value * v = state.allocValue();
             if (arg == "--arg")
-                state.eval(parseExprFromString(state, value, absPath(".")), v);
+                state.eval(parseExprFromString(state, value, absPath(".")), *v);
             else
-                mkString(v, value);
+                mkString(*v, value);
             autoArgs[state.symbols.create(name)].push_back(v);
         }
         else if (arg == "--gc-roots-dir") {
@@ -239,6 +241,7 @@ void run(Strings args)
     Value v;
     state.mkThunk_(v, e);
 
+    std::cout.setf(std::ios::unitbuf);
     XMLWriter doc(true, std::cout);
     XMLOpenElement root(doc, "jobs");
     findJobs(state, doc, ArgsUsed(), autoArgs, v, "");
diff --git a/src/script/hydra_update_gc_roots.pl.in b/src/script/hydra_update_gc_roots.pl.in
index a07d4690..890f6138 100755
--- a/src/script/hydra_update_gc_roots.pl.in
+++ b/src/script/hydra_update_gc_roots.pl.in
@@ -36,34 +36,43 @@ sub keepBuild {
 
 foreach my $project ($db->resultset('Projects')->all) {
 
-    # Go over all jobs in this project.
+    # Go over all jobsets in this project.
+    foreach my $jobset ($project->jobsets->all) {
+        my $keepnr = $jobset->keepnr;
 
-    foreach my $job ($project->jobs->all) {
-        print STDERR "*** looking for builds to keep in job ",
-            $project->name, ":", $job->jobset->name, ":", $job->name, "\n";
+	# If the jobset has been disabled for more than one week, than
+	# don't keep its builds anymore.
+	if ($jobset->enabled == 0 && (time() - $jobset->lastcheckedtime > (7 * 24 * 3600))) {
+	    print STDERR "*** skipping disabled jobset ", $project->name, ":", $jobset->name, "\n";
+	    next;
+	}
+        
+        # Go over all jobs in this jobset.
+        foreach my $job ($jobset->jobs->all) {
+            print STDERR "*** looking for builds to keep in job ",
+                $project->name, ":", $job->jobset->name, ":", $job->name, "\n";
 
-        # Keep the N most recent successful builds for each job and
-        # platform.
-        # !!! Take time into account? E.g. don't delete builds that
-        # are younger than N days.
-	my @systems = $job->builds->search({ }, { select => ["system"], distinct => 1 })->all;
-    my $keepnr = $job->jobset->keepnr ;
-	foreach my $system (@systems) {
-            my @recentBuilds = $job->builds->search(
-		{ finished => 1
-                , buildStatus => 0 # == success
-                , system => $system->system
-                },
-                { join => 'resultInfo'
-                , order_by => 'id DESC'
-                , rows => $keepnr
-                });
-	    keepBuild $_ foreach @recentBuilds;
+            # Keep the N most recent successful builds for each job
+            # and platform.
+            # !!! Take time into account? E.g. don't delete builds
+            # that are younger than N days.
+            my @systems = $job->builds->search({ }, { select => ["system"], distinct => 1 })->all;
+            foreach my $system (@systems) {
+                my @recentBuilds = $job->builds->search(
+                    { finished => 1
+                    , buildStatus => 0 # == success
+                    , system => $system->system
+                    },
+                    { join => 'resultInfo'
+                    , order_by => 'id DESC'
+                    , rows => $keepnr
+                    });
+                keepBuild $_ foreach @recentBuilds;
+	    }
 	}
     }
 
     # Go over all views in this project.
-
     foreach my $view ($project->views->all) {
         print STDERR "*** looking for builds to keep in view ", $project->name, ":", $view->name, "\n";