int64_t offset = result.size();
    int64_t size = buffer.size();
    uint64_t hash = tsl::Fingerprint64(buffer);
    if (hashcode_to_pos.find(hash) == hashcode_to_pos.end()) {
      hashcode_to_pos[hash] = std::make_pair(offset, size);
      buffer_idx_map_[index] = std::make_pair(offset, size);
      result.Append(std::move(buffer));
      // Pad to be 16 bytes aligned.
      {