final void init(ReaderPool readerPool, MergePolicy.OneMerge merge, MergeState mergeState, boolean initWritableLiveDocs) throws IOException {
      if (mergedDeletesAndUpdates == null) {
        mergedDeletesAndUpdates = readerPool.get(merge.info, true);
        docMap = merge.getDocMap(mergeState);
        assert docMap.isConsistent(merge.info.info.maxDoc());
      }
      if (initWritableLiveDocs && !initializedWritableLiveDocs) {
        mergedDeletesAndUpdates.initWritableLiveDocs();
        this.initializedWritableLiveDocs = true;
      }
    }