def prune_cache(mtime=15)
      # get old, unused entries and discard from DB and filesystem
      entries = remove_old_items(mtime)
      entries.each do |key, entry|
        FileUtils.rm_f(entry[:file])
      end
    end
def prune_cache(mtime=15)
      # get old, unused entries and discard from DB and filesystem
      entries = remove_old_items(mtime)
      entries.each do |key, entry|
        FileUtils.rm_f(entry[:file])
      end
    end
the fastest way to prune this is to use the local find command