be/src/exec/union-node.h

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//
//   http://www.apache.org/licenses/LICENSE-2.0
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#ifndef IMPALA_EXEC_UNION_NODE_H_
#define IMPALA_EXEC_UNION_NODE_H_

#include <boost/scoped_ptr.hpp>

#include "exec/exec-node.h"
#include "runtime/row-batch.h"

namespace impala {

class DescriptorTbl;
class ExprContext;
class RuntimeState;
class Tuple;
class TupleRow;
class TPlanNode;

/// Node that merges the results of its children by materializing their
/// evaluated expressions into row batches. The UnionNode pulls row batches from its
/// children sequentially, i.e., it exhausts one child completely before moving
/// on to the next one.
class UnionNode : public ExecNode {
 public:
  UnionNode(ObjectPool* pool, const TPlanNode& tnode, const DescriptorTbl& descs);

  virtual Status Init(const TPlanNode& tnode, RuntimeState* state);
  virtual Status Prepare(RuntimeState* state);
  virtual Status Open(RuntimeState* state);
  virtual Status GetNext(RuntimeState* state, RowBatch* row_batch, bool* eos);
  virtual Status Reset(RuntimeState* state);
  virtual void Close(RuntimeState* state);

 private:
  /// Tuple id resolved in Prepare() to set tuple_desc_;
  const int tuple_id_;

  /// Descriptor for tuples this union node constructs.
  const TupleDescriptor* tuple_desc_;

  /// Const exprs materialized by this node. These exprs don't refer to any children.
  /// Only materialized by the first fragment instance to avoid duplication.
  std::vector<std::vector<ExprContext*>> const_expr_lists_;

  /// Exprs materialized by this node. The i-th result expr list refers to the i-th child.
  std::vector<std::vector<ExprContext*>> child_expr_lists_;

  /////////////////////////////////////////
  /// BEGIN: Members that must be Reset()

  /// Index of current child.
  int child_idx_;

  /// Current row batch of current child. We reset the pointer to a new RowBatch
  /// when switching to a different child.
  boost::scoped_ptr<RowBatch> child_batch_;

  /// Index of current row in child_row_batch_.
  int child_row_idx_;

  /// Saved from the last to GetNext() on the current child.
  bool child_eos_;

  /// Index of current const result expr list.
  int const_expr_list_idx_;

  /// END: Members that must be Reset()
  /////////////////////////////////////////

  /// Opens the child at child_idx_, fetches the first batch into child_row_batch_,
  /// and sets child_row_idx_ to 0. May set child_eos_.
  Status OpenCurrentChild(RuntimeState* state);

  /// Evaluates 'exprs' over 'row', materializes the results in 'tuple_buf'.
  /// and appends the new tuple to 'dst_batch'. Increments 'num_rows_returned_'.
  inline void MaterializeExprs(const std::vector<ExprContext*>& exprs,
      TupleRow* row, uint8_t* tuple_buf, RowBatch* dst_batch);
};

}

#endif