Function TestHistogramExternalMemory

tests/cpp/tree/hist/test_histogram.cc:410–501

}
namespace {
void TestHistogramExternalMemory(Context const *ctx, BatchParam batch_param, bool is_approx,
                                 bool force_read_by_column) {
  size_t constexpr kEntries = 1 << 16;
  auto m =
      RandomDataGenerator{kEntries / 8, 8, 0.0f}.Batches(4).GenerateSparsePageDMatrix("temp", true);

  std::vector<float> hess(m->Info().num_row_, 1.0);
  if (is_approx) {
    batch_param.hess = hess;
  }

  std::vector<bst_idx_t> partition_size(1, 0);
  bst_bin_t total_bins{0};
  bst_idx_t n_samples{0};

  auto gpair = GenerateRandomGradients(m->Info().num_row_, 0.0, 1.0);
  auto const &h_gpair = gpair.HostVector();

  RegTree tree;
  std::vector<bst_node_t> nodes{RegTree::kRoot};
  common::BlockedSpace2d space{
      1, [&](std::size_t nidx_in_set) { return partition_size.at(nidx_in_set); }, 256};

  common::GHistRow multi_page;
  HistogramBuilder multi_build;
  HistMakerTrainParam hist_param;
  std::vector<bst_node_t> dummy_sub;
  {
    /**
     * Multi page
     */
    std::vector<common::RowSetCollection> rows_set;
    for (auto const &page : m->GetBatches<GHistIndexMatrix>(ctx, batch_param)) {
      CHECK_LT(page.base_rowid, m->Info().num_row_);
      auto n_rows_in_node = page.Size();
      partition_size[0] = std::max(partition_size[0], n_rows_in_node);
      total_bins = page.cut.TotalBins();
      n_samples += n_rows_in_node;

      rows_set.emplace_back();
      InitRowPartitionForTest(&rows_set.back(), n_rows_in_node, page.base_rowid);
    }
    ASSERT_EQ(n_samples, m->Info().num_row_);

    multi_build.Reset(ctx, total_bins, batch_param, false, false, &hist_param);
    multi_build.AddHistRows(tree.HostScView(), &nodes, &dummy_sub, false);
    std::size_t page_idx{0};
    for (auto const &page : m->GetBatches<GHistIndexMatrix>(ctx, batch_param)) {
      multi_build.BuildHist(page_idx, space, page, rows_set[page_idx], nodes,
                            linalg::MakeTensorView(ctx, h_gpair, h_gpair.size()),
                            force_read_by_column);
      ++page_idx;
    }
    multi_build.SyncHistogram(ctx, tree.HostScView(), nodes, {});

    multi_page = multi_build.Histogram()[RegTree::kRoot];
  }