code: public void optimize() {
          Log.debug("Optimizing index");
          try {
              indexWriter.forceMerge(1, true);
              indexWriter.commit();
          } catch (IOException e) {
              Log.error(e, "Error while optimizing index");
              throw new RuntimeException(e);
          }
      }
docs: Optimizes the index forcing merge segments leaving one single segment. This operation blocks until all merging
  completes.