be/src/exec/parquet/parquet-collection-column-reader.h

// Licensed to the Apache Software Foundation (ASF) under one
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// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
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// specific language governing permissions and limitations
// under the License.

#pragma once

#include <vector>

#include "exec/parquet/parquet-column-readers.h"

namespace impala {

/// Collections are not materialized directly in parquet files; only scalar values appear
/// in the file. CollectionColumnReader uses the definition and repetition levels of child
/// column readers to figure out the boundaries of each collection in this column.
class CollectionColumnReader : public ParquetColumnReader {
 public:
  CollectionColumnReader(
      HdfsParquetScanner* parent, const SchemaNode& node, const SlotDescriptor* slot_desc)
    : ParquetColumnReader(parent, node, slot_desc) {
    DCHECK(node_.is_repeated());
    if (slot_desc != nullptr) DCHECK(slot_desc->type().IsCollectionType());
  }

  virtual ~CollectionColumnReader() {}

  vector<ParquetColumnReader*>* children() { return &children_; }

  virtual bool IsCollectionReader() const override { return true; }

  /// The repetition level indicating that the current value is the first in a new
  /// collection (meaning the last value read was the final item in the previous
  /// collection).
  int new_collection_rep_level() const { return max_rep_level() - 1; }

  /// Materializes CollectionValue into tuple slot (if materializing) and advances to next
  /// value.
  virtual bool ReadValue(MemPool* pool, Tuple* tuple) override;

  /// Same as ReadValue but does not advance repetition level. Only valid for columns not
  /// in collections.
  virtual bool ReadNonRepeatedValue(MemPool* pool, Tuple* tuple) override;

  /// Implementation of ReadValueBatch for collections.
  virtual bool ReadValueBatch(MemPool* pool, int max_values, int tuple_size,
      uint8_t* tuple_mem, int* num_values) override;

  /// Implementation of ReadNonRepeatedValueBatch() for collections.
  virtual bool ReadNonRepeatedValueBatch(MemPool* pool, int max_values, int tuple_size,
      uint8_t* tuple_mem, int* num_values) override;

  /// Advances all child readers to the beginning of the next collection and updates this
  /// reader's state.
  virtual bool NextLevels() override;

  /// This is called once for each row group in the file.
  void Reset() {
    def_level_ = ParquetLevel::INVALID_LEVEL;
    rep_level_ = ParquetLevel::INVALID_LEVEL;
    pos_current_value_ = ParquetLevel::INVALID_POS;
  }

  virtual void Close(RowBatch* row_batch) override;

 private:
  /// Column readers of fields contained within this collection. There is at least one
  /// child reader per collection reader. Child readers either materialize slots in the
  /// collection item tuples, or there is a single child reader that does not materialize
  /// any slot and is only used by this reader to read def and rep levels.
  vector<ParquetColumnReader*> children_;

  /// Updates this reader's def_level_, rep_level_, and pos_current_value_ based on child
  /// reader's state.
  void UpdateDerivedState();

  /// Recursively reads from children_ to assemble a single CollectionValue into
  /// 'slot'. Also advances rep_level_ and def_level_ via NextLevels().
  ///
  /// Returns false if execution should be aborted for some reason, e.g. parse_error_ is
  /// set, the query is cancelled, or the scan node limit was reached. Otherwise returns
  /// true.
  inline bool ReadSlot(CollectionValue* slot, MemPool* pool);
};
} // namespace impala