docs: void map(ByteBuffer buffer) {
      if (!(reader instanceof MappedJournalSegmentReader)) {
        JournalReader<E> reader = this.reader;
        this.reader = new MappedJournalSegmentReader<>(buffer, segment, maxEntrySize, index, namespace);
        this.reader.reset(reader.getNextIndex());
        reader.close();
      }
    }