be/src/exec/streaming-aggregation-node.h

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#ifndef IMPALA_EXEC_STREAMING_AGGREGATION_NODE_H
#define IMPALA_EXEC_STREAMING_AGGREGATION_NODE_H

#include <memory>

#include "exec/aggregation-node-base.h"

namespace impala {

class RowBatch;
class RuntimeState;

/// Node for doing streaming partitioned hash aggregation.
///
/// This node consumes the input from child(0) during GetNext() and then passes it to the
/// Aggregator, which does the actual work of aggregating. The aggregator will attempt to
/// aggregate the rows into its hash table, but if there is not enough memory available or
/// if the reduction from the aggregation is not very good, it will 'stream' the rows
/// through and return them without aggregating them instead of spilling. After all of the
/// input as been processed from child(0), subsequent calls to GetNext() will return any
/// rows that were aggregated in the Aggregator's hash table.
///
/// Since the rows returned by GetNext() may be only partially aggregated if there are
/// memory contraints, this is a preliminary aggregation step that functions as an
/// optimization and will always be followed in the plan by an AggregationNode that does
/// the final aggregation.
///
/// This node only supports grouping aggregations.
class StreamingAggregationNode : public AggregationNodeBase {
 public:
  StreamingAggregationNode(
      ObjectPool* pool, const TPlanNode& tnode, const DescriptorTbl& descs);

  virtual Status Open(RuntimeState* state) override;
  virtual Status GetNext(RuntimeState* state, RowBatch* row_batch, bool* eos) override;
  virtual Status Reset(RuntimeState* state, RowBatch* row_batch) override;
  virtual void Close(RuntimeState* state) override;

  virtual void DebugString(int indentation_level, std::stringstream* out) const override;

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

  /// Row batch retrieved from the child and passed to Aggregators in GetNext(). Stored
  /// here as we may need it in multiple GetNext() calls if we're streaming rows through.
  std::unique_ptr<RowBatch> child_batch_;

  /// If true, there are no more rows in 'child_batch_' that need to be passed to any
  /// Aggregator, and the next call to GetNext() will retrieve another batch, unless
  /// 'child_eos_' is true.
  bool child_batch_processed_ = true;

  /// True if no more rows to process from child.
  bool child_eos_ = false;

  /// If 'replicate_input_' is true, the index in 'aggs_' of the next Aggregator to pass
  /// 'child_batch_' into.
  int32_t replicate_agg_idx_ = 0;

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

  /// Get output rows from child for streaming pre-aggregation. Aggregates some rows with
  /// hash table and passes through other rows converted into the intermediate
  /// tuple format. Sets 'child_eos_' once all rows from child have been returned.
  Status GetRowsStreaming(RuntimeState* state, RowBatch* row_batch) WARN_UNUSED_RESULT;
};
} // namespace impala

#endif // IMPALA_EXEC_STREAMING_AGGREGATION_NODE_H