src/kudu/common/iterator_stats.h

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// 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
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.
#ifndef KUDU_COMMON_ITERATOR_STATS_H
#define KUDU_COMMON_ITERATOR_STATS_H

#include <cstdint>
#include <string>

namespace kudu {

struct IteratorStats {
  IteratorStats();

  std::string ToString() const;

  // The number of cells which were read from disk --  regardless of whether
  // they were decoded/materialized.
  int64_t cells_read;

  // The number of bytes read from disk (or cache) by the iterator.
  int64_t bytes_read;

  // The number of CFile data blocks read from disk (or cache) by the iterator.
  int64_t blocks_read;

  // The number of column predicates disabled because they were determined to be
  // ineffective.
  // There is only one predicate per column (if any) so for a per column stat this would be 0 or 1.
  // Using an integer helps the stat work well when aggregating or computing delta.
  int64_t predicates_disabled;

  // Add statistics contained 'other' to this object (for each field
  // in this object, increment it by the value of the equivalent field
  // in 'other').
  IteratorStats& operator+=(const IteratorStats& other);
  IteratorStats& operator-=(const IteratorStats& other);

  IteratorStats operator+(const IteratorStats& other);
  IteratorStats operator-(const IteratorStats& other);

 private:
  // DCHECK that all of the stats are non-negative. This is a no-op in
  // release builds.
  void DCheckNonNegative() const;
};

} // namespace kudu

#endif