Method peelEncodings

bolt/expression/Expr.cpp:988–1062

  // its a shared subexpression.
  const auto& rowsToPeel =
      context.isFinalSelection() ? rows : *context.finalSelection();
  auto numFields = context.row()->childrenSize();
  std::vector<VectorPtr> vectorsToPeel;
  vectorsToPeel.reserve(distinctFields_.size());
  for (auto* field : distinctFields_) {
    auto fieldIndex = field->index(context);
    assert(fieldIndex >= 0 && fieldIndex < numFields);
    auto fieldVector = context.getField(fieldIndex);
    if (fieldVector->isConstantEncoding()) {
      // Make sure constant encoded fields are loaded
      fieldVector = context.ensureFieldLoaded(fieldIndex, rowsToPeel);
    }
    vectorsToPeel.push_back(fieldVector);
  }

  // Attempt peeling.
  BOLT_CHECK(!vectorsToPeel.empty());
  std::vector<VectorPtr> peeledVectors;
  auto peeledEncoding = PeeledEncoding::peel(
      vectorsToPeel, rowsToPeel, localDecoded, propagatesNulls_, peeledVectors);

  if (!peeledEncoding) {
    return Expr::PeelEncodingsResult::empty();
  }

  // Translate the relevant rows.
  SelectivityVector* newFinalSelection = nullptr;
  if (!context.isFinalSelection()) {
    newFinalSelection = peeledEncoding->translateToInnerRows(
        *context.finalSelection(), finalRowsHolder);
  }
  auto newRows = peeledEncoding->translateToInnerRows(rows, newRowsHolder);

  // Save context and set the peel, peeled fields and final selection (if
  // applicable).
  context.saveAndReset(saver, rows);
  context.setPeeledEncoding(peeledEncoding);
  if (newFinalSelection) {
    *context.mutableFinalSelection() = newFinalSelection;
  }
  DCHECK_EQ(peeledVectors.size(), distinctFields_.size());
  for (int i = 0; i < peeledVectors.size(); ++i) {
    auto fieldIndex = distinctFields_[i]->index(context);
    context.setPeeled(fieldIndex, peeledVectors[i]);
  }

  // If the expression depends on one dictionary, results are cacheable.
  bool mayCache = false;
  if (context.cacheEnabled()) {
    mayCache = distinctFields_.size() == 1 &&
        VectorEncoding::isDictionary(context.wrapEncoding()) &&
        !peeledVectors[0]->memoDisabled();
  }

  BOLT_TEST_ADJUST(
      "bytedance::bolt::exec::Expr::peelEncodings::mayCache", &mayCache);
  return {newRows, finalRowsHolder.get(), mayCache};
}