compare_access_paths.h

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#ifndef SQL_JOIN_OPTIMIZER_COMPARE_ACCESS_PATHS_H
#define SQL_JOIN_OPTIMIZER_COMPARE_ACCESS_PATHS_H
 
#include <assert.h>
#include <stdint.h>
 
#include <cmath>
 
#include "sql/join_optimizer/access_path.h"
#include "sql/join_optimizer/interesting_orders.h"
 
enum class FuzzyComparisonResult : uint32_t {
  IDENTICAL = 0,
  FIRST_BETTER = 1,
  SECOND_BETTER = 2,
  FIRST_SLIGHTLY_BETTER = 4,
  SECOND_SLIGHTLY_BETTER = 8
};
 
// Compare x and y with a given fuzz factor under the assumption that the
// lesser value is preferred. If the relative difference between x and y
// is small (x and y are fuzzily identical) we still return information
// about which one is slightly better.
inline FuzzyComparisonResult FuzzyComparison(double x, double y,
                                             double fuzz_factor) {
  assert(std::isfinite(x));
  assert(std::isfinite(y));
  assert(x >= 0);
  assert(y >= 0);
 
  if (fuzz_factor * x < y) {
    return FuzzyComparisonResult::FIRST_BETTER;
  } else if (fuzz_factor * y < x) {
    return FuzzyComparisonResult::SECOND_BETTER;
  } else {  // Fuzzily identical
    if (x < y) {
      return FuzzyComparisonResult::FIRST_SLIGHTLY_BETTER;
    } else if (y < x) {
      return FuzzyComparisonResult::SECOND_SLIGHTLY_BETTER;
    } else {
      return FuzzyComparisonResult::IDENTICAL;
    }
  }
}
 
enum class PathComparisonResult {
  FIRST_DOMINATES,
  SECOND_DOMINATES,
  DIFFERENT_STRENGTHS,
  IDENTICAL,
};
 
PathComparisonResult CompareAccessPaths(const LogicalOrderings &orderings,
                                        const AccessPath &a,
                                        const AccessPath &b,
                                        OrderingSet obsolete_orderings);
 
#endif  // SQL_JOIN_OPTIMIZER_COMPARE_ACCESS_PATHS_H