docs: private String getGnuplotBasePath(final TSDB tsdb, final HttpQuery query) {
      final Map<String, List<String>> q = query.getQueryString();
      q.remove("ignore");
      // Super cheap caching mechanism: hash the query string.
      final HashMap<String, List<String>> qs =
        new HashMap<String, List<String>>(q);
      // But first remove the parameters that don't influence the output.
      qs.remove("png");
      qs.remove("json");
      qs.remove("ascii");
      return tsdb.getConfig().getDirectoryName("tsd.http.cachedir") +
          Integer.toHexString(qs.hashCode());
    }