Method GetNext

be/src/runtime/sorter.cc:505–603

template <bool CONVERT_OFFSET_TO_PTR>
Status Sorter::Run::GetNext(RowBatch* output_batch, bool* eos) {
  // Var-len offsets are converted only when reading var-len data from unpinned runs.
  // We shouldn't convert var len offsets if there are no pages, since in that case
  // they must all be null or zero-length strings, which don't point into a valid page.
  DCHECK_EQ(CONVERT_OFFSET_TO_PTR, HasVarLenPages() && !is_pinned_);

  if (end_of_fixed_len_page_
      && fixed_len_pages_index_ >= static_cast<int>(fixed_len_pages_.size()) - 1) {
    // All pages were previously attached to output batches. GetNextBatch() assumes
    // that we don't attach resources to the batch on eos.
    DCHECK_EQ(NumOpenPages(fixed_len_pages_), 0);
    DCHECK_EQ(NumOpenPages(var_len_pages_), 0);

    CloseAllPages();
    *eos = true;
    DCHECK_EQ(num_tuples_returned_, num_tuples_);
    return Status::OK();
  }

  // Advance the fixed or var len page if we reached the end in the previous call to
  // GetNext().
  if (end_of_fixed_len_page_) {
    RETURN_IF_ERROR(PinNextReadPage(&fixed_len_pages_, fixed_len_pages_index_));
    ++fixed_len_pages_index_;
    fixed_len_page_offset_ = 0;
    end_of_fixed_len_page_ = false;
  }
  if (end_of_var_len_page_) {
    RETURN_IF_ERROR(PinNextReadPage(&var_len_pages_, var_len_pages_index_));
    ++var_len_pages_index_;
    end_of_var_len_page_ = false;
  }

  // Fills rows into the output batch until a page boundary is reached.
  Page* fixed_len_page = &fixed_len_pages_[fixed_len_pages_index_];
  DCHECK(fixed_len_page != nullptr);

  // Ensure we have a reference to the fixed-length page's buffer.
  RETURN_IF_ERROR(fixed_len_page->WaitForBuffer());

  // If we're converting offsets into unpinned var-len pages, make sure the
  // current var-len page is in memory.
  if (CONVERT_OFFSET_TO_PTR && HasVarLenPages()) {
    RETURN_IF_ERROR(var_len_pages_[var_len_pages_index_].WaitForBuffer());
  }

  while (!output_batch->AtCapacity()
      && fixed_len_page_offset_ < fixed_len_page->valid_data_len()) {
    DCHECK(fixed_len_page != nullptr);
    Tuple* input_tuple =
        reinterpret_cast<Tuple*>(fixed_len_page->data() + fixed_len_page_offset_);

    if (CONVERT_OFFSET_TO_PTR && !ConvertOffsetsToPtrs(input_tuple, *sort_tuple_desc_)) {
      DCHECK(!is_pinned_);
      // The var-len data is in the next page. We are done with the current page, so
      // return rows we've accumulated so far along with the page's buffer and advance
      // to the next page in the next GetNext() call. We need the page's reservation to
      // pin the next page, so flush resources.