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/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/platform/basic.h"
#include "mongo/db/query/sbe_plan_ranker.h"
namespace mongo::sbe::plan_ranker {
namespace {
/**
* A plan ranker for the SBE plan stage tree. Defines productivity as a cumulative number of
* physical reads from the storage performed by all stages in the plan which can read from the
* storage, divided by the total number of advances of the root stage, which corresponds to the
* number of returned documents.
*/
class DefaultPlanScorer final : public mongo::plan_ranker::PlanScorer<PlanStageStats> {
public:
DefaultPlanScorer(const QuerySolution* solution) : _solution{solution} {
invariant(_solution);
}
protected:
double calculateProductivity(const mongo::sbe::PlanStageStats* root) const final {
return plan_ranker::calculateProductivity(root->common.advances,
calculateNumberOfReads(root));
}
std::string getProductivityFormula(const mongo::sbe::PlanStageStats* root) const final {
auto numReads{calculateNumberOfReads(root)};
StringBuilder sb;
sb << "(" << (root->common.advances) << " advances + 1)/(" << numReads << " numReads + 1)";
return sb.str();
}
double getNumberOfAdvances(const mongo::sbe::PlanStageStats* stats) const final {
return stats->common.advances;
}
bool hasStage(StageType type, const mongo::sbe::PlanStageStats* stats) const final {
// In SBE a plan stage doesn't map 1-to-1 to a solution node, and can expand into a subtree
// of plan stages, each having its own plan stage stats. So, to answer whether an SBE plan
// stage stats tree contains a stage of the given 'type', we need to look into the solution
// tree instead.
return _solution->hasNode(type);
}
private:
const QuerySolution* _solution;
};
} // namespace
std::unique_ptr<mongo::plan_ranker::PlanScorer<PlanStageStats>> makePlanScorer(
const QuerySolution* solution) {
return std::make_unique<DefaultPlanScorer>(solution);
}
double calculateProductivity(const size_t advances, const size_t numReads) {
// We add one to the number of advances so that plans which returned zero documents still
// have a productivity of non-zero. This allows us to compare productivity scores between
// plans with zero advances. For example, a plan which did zero advances but examined ten
// documents would have a score of (0 + 1)/10, while a plan which did zero advances but
// examined a hundred documents would have a score of (0 + 1)/100.
//
// Similarly, we add one to the number of reads in case 0 reads were performed. This could
// happen if a plan encounters EOF right away, for example.
return static_cast<double>(advances + 1) / static_cast<double>(numReads + 1);
}
} // namespace mongo::sbe::plan_ranker
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