alter table builds add column isCurrent integer default 0;

        # Have we already done this build (in this job)?  Don't do it
        # again unless it has been garbage-collected.  The latest
        # builds for each platforms are GC roots, so they shouldn't be
        # GCed.  However, if a job has reverted to a previous state,
        # it's possible that a GCed build becomes current again.  In
        # that case we have to rebuild it to ensure that it appears in
        # channels etc.
        my @previousBuilds = $jobInDB->builds->search({outPath => $outPath}, {order_by => "id"});

        # Don't add a build that has already been scheduled for this
        # job, or has been built but is still a "current" build for
        # this job.  Note that this means that if the sources of a job
        # are changed from A to B and then reverted to A, three builds
        # will be performed (though the last one will probably use the
        # cached result from the first).  This ensures that the builds
        # with the highest ID will always be the ones that we want in
        # the channels.
        # !!! Checking $drvPath doesn't take meta-attributes into
        # account.  For instance, do we want a new build to be
        # scheduled if the meta.maintainers field is changed?
        my @previousBuilds = $jobInDB->builds->search({drvPath => $drvPath, isCurrent => 1});

            foreach my $build (@previousBuilds) {
                if (!$build->finished) {
                    print "already scheduled as build ", $build->id, "\n";
                    $currentBuilds->{$build->id} = 1;
                    return;
                }
            }
            if (isValidPath($outPath)) {
                print "already done as build ", $previousBuilds[0]->id, "\n";
                # Mark the previous build as "current" so that it will
                # appear in the "latest" channel for this
                # project/jobset/job.
                $previousBuilds[0]->update({iscurrent => 1});
                $currentBuilds->{$previousBuilds[0]->id} = 1;
                return;
            }
            print "already done as build ", $previousBuilds[0]->id,
                "; rebuilding because it was garbage-collected\n";

            print "already scheduled/built\n";
            $currentBuilds->{$_->id} = 1 foreach @previousBuilds;
            return;

            print "current is ", $build->id, "\n";