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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.
*/
#pragma once
#include "mongo/db/query/plan_explainer_factory.h"
#include "mongo/db/query/plan_ranker.h"
// Forward declarations.
namespace mongo::sbe::plan_ranker {
std::unique_ptr<mongo::plan_ranker::PlanScorer<PlanStageStats>> makePlanScorer(
const QuerySolution* solution);
} // namespace mongo::sbe::plan_ranker
namespace mongo::plan_ranker {
/**
* A factory function to create a plan scorer for a plan stage stats tree.
*/
std::unique_ptr<PlanScorer<PlanStageStats>> makePlanScorer();
/**
* Returns a PlanRankingDecision which has the ranking and the information about the ranking
* process with status OK if everything worked. 'candidateOrder' within the PlanRankingDecision
* holds indices into candidates ordered by score (winner in first element).
*
* Returns an error if there was an issue with plan ranking (e.g. there was no viable plan).
*/
template <typename PlanStageStatsType, typename PlanStageType, typename ResultType, typename Data>
StatusWith<std::unique_ptr<PlanRankingDecision>> pickBestPlan(
const std::vector<BaseCandidatePlan<PlanStageType, ResultType, Data>>& candidates) {
invariant(!candidates.empty());
// A plan that hits EOF is automatically scored above
// its peers. If multiple plans hit EOF during the same
// set of round-robin calls to work(), then all such plans
// receive the bonus.
double eofBonus = 1.0;
// Get stat trees from each plan.
std::vector<std::unique_ptr<PlanStageStatsType>> statTrees;
for (size_t i = 0; i < candidates.size(); ++i) {
if constexpr (std::is_same_v<PlanStageStatsType, PlanStageStats>) {
statTrees.push_back(candidates[i].root->getStats());
} else {
statTrees.push_back(candidates[i].root->getStats(false /* includeDebugInfo */));
}
}
// Holds (score, candidateIndex).
// Used to derive scores and candidate ordering.
std::vector<std::pair<double, size_t>> scoresAndCandidateIndices;
std::vector<size_t> failed;
// Compute score for each tree. Record the best.
for (size_t i = 0; i < statTrees.size(); ++i) {
auto explainer = [&]() {
if constexpr (std::is_same_v<PlanStageStatsType, PlanStageStats>) {
return plan_explainer_factory::make(candidates[i].root,
candidates[i].solution->_enumeratorExplainInfo);
} else {
static_assert(std::is_same_v<PlanStageStatsType, mongo::sbe::PlanStageStats>);
return plan_explainer_factory::make(candidates[i].root.get(),
&candidates[i].data.stageData,
candidates[i].solution.get());
}
}();
if (candidates[i].status.isOK()) {
log_detail::logScoringPlan([&]() { return candidates[i].solution->toString(); },
[&]() {
auto&& [stats, _] = explainer->getWinningPlanStats(
ExplainOptions::Verbosity::kExecStats);
return stats.jsonString(ExtendedRelaxedV2_0_0, true);
},
[&]() { return explainer->getPlanSummary(); },
i,
statTrees[i]->common.isEOF);
auto scorer = [solution = candidates[i].solution.get()]()
-> std::unique_ptr<PlanScorer<PlanStageStatsType>> {
if constexpr (std::is_same_v<PlanStageStatsType, PlanStageStats>) {
return makePlanScorer();
} else {
static_assert(std::is_same_v<PlanStageStatsType, mongo::sbe::PlanStageStats>);
return sbe::plan_ranker::makePlanScorer(solution);
}
}();
double score = scorer->calculateScore(statTrees[i].get());
log_detail::logScore(score);
if (statTrees[i]->common.isEOF) {
log_detail::logEOFBonus(eofBonus);
score += 1;
}
candidates[i].solution->score = score;
scoresAndCandidateIndices.push_back(std::make_pair(score, i));
} else {
failed.push_back(i);
log_detail::logFailedPlan([&] { return explainer->getPlanSummary(); });
}
}
// If there isn't a viable plan we should error.
if (scoresAndCandidateIndices.size() == 0U) {
return {ErrorCodes::Error(31157),
"No viable plan was found because all candidate plans failed."};
}
// Sort (scores, candidateIndex). Get best child and populate candidate ordering.
std::stable_sort(scoresAndCandidateIndices.begin(),
scoresAndCandidateIndices.end(),
[](const auto& lhs, const auto& rhs) {
// Just compare score in lhs.first and rhs.first;
// Ignore candidate array index in lhs.second and rhs.second.
return lhs.first > rhs.first;
});
auto why = std::make_unique<PlanRankingDecision>();
if constexpr (std::is_same_v<PlanStageStatsType, mongo::sbe::PlanStageStats>) {
// For SBE, we need to store a serialized winning plan within the ranking decision to be
// able to included it into the explain output for a cached plan stats, since we cannot
// reconstruct it from a PlanStageStats tree.
// Get the winning candidate's index to get the correct winning plan.
size_t winnerIdx = scoresAndCandidateIndices[0].second;
auto explainer = plan_explainer_factory::make(candidates[winnerIdx].root.get(),
&candidates[winnerIdx].data.stageData,
candidates[winnerIdx].solution.get());
auto&& [stats, _] =
explainer->getWinningPlanStats(ExplainOptions::Verbosity::kQueryPlanner);
SBEStatsDetails details;
details.serializedWinningPlan = std::move(stats);
why->stats = std::move(details);
} else {
static_assert(std::is_same_v<PlanStageStatsType, PlanStageStats>);
why->stats = StatsDetails{};
}
// Update results in 'why'
// Stats and scores in 'why' are sorted in descending order by score.
auto&& stats = why->getStats<PlanStageStatsType>();
why->failedCandidates = std::move(failed);
for (size_t i = 0; i < scoresAndCandidateIndices.size(); ++i) {
double score = scoresAndCandidateIndices[i].first;
size_t candidateIndex = scoresAndCandidateIndices[i].second;
stats.candidatePlanStats.push_back(std::move(statTrees[candidateIndex]));
why->scores.push_back(score);
why->candidateOrder.push_back(candidateIndex);
}
for (auto& i : why->failedCandidates) {
stats.candidatePlanStats.push_back(std::move(statTrees[i]));
}
return StatusWith<std::unique_ptr<PlanRankingDecision>>(std::move(why));
}
} // namespace mongo::plan_ranker
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