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/**
* Copyright (C) 2018-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 <queue>
#include "mongo/db/exec/plan_stats.h"
#include "mongo/db/exec/sbe/stages/plan_stats.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/query/explain.h"
#include "mongo/db/query/plan_ranking_decision.h"
#include "mongo/db/query/query_solution.h"
#include "mongo/util/container_size_helper.h"
namespace mongo::plan_ranker {
// The logging facility enforces the rule that logging should not be done in a header file. Since
// template classes and functions below must be defined in the header file and since they use the
// logging facility, we have to define the helper functions below to perform the actual logging
// operation from template code.
// Note that we pass std::function callback instead of string values to avoid spending time
// generating log output that may never actually be written to the logs, depending on the current
// log level.
namespace log_detail {
void logScoreFormula(std::function<std::string()> formula,
double score,
double baseScore,
double productivity,
double noFetchBonus,
double noSortBonus,
double noIxisectBonus,
double tieBreakers);
void logScoreBoost(double score);
void logScoringPlan(std::function<std::string()> solution,
std::function<std::string()> explain,
std::function<std::string()> planSummary,
size_t planIndex,
bool isEOF);
void logScore(double score);
void logEOFBonus(double eofBonus);
void logFailedPlan(std::function<std::string()> planSummary);
} // namespace log_detail
/**
* Assigns the stats tree a 'goodness' score. The higher the score, the better the plan. The exact
* value isn't meaningful except for imposing a ranking.
*
* All specific plan scorers should inherit from this scorer and provide methods to produce the plan
* productivity factor, and the number of plan "advances", representing the number of documents
* returned by the PlanStage tree.
*/
template <typename PlanStageStatsType>
class PlanScorer {
public:
PlanScorer() = default;
virtual ~PlanScorer() = default;
double calculateScore(const PlanStageStatsType* stats) const {
// We start all scores at 1. Our "no plan selected" score is 0 and we want all plans to
// be greater than that.
const double baseScore = 1;
const auto productivity = calculateProductivity(stats);
const auto advances = getNumberOfAdvances(stats);
const double epsilon =
std::min(1.0 / static_cast<double>(10 * (advances > 0 ? advances : 1)), 1e-4);
// We prefer queries that don't require a fetch stage.
double noFetchBonus = epsilon;
if (hasStage(STAGE_FETCH, stats)) {
noFetchBonus = 0;
}
// In the case of ties, prefer solutions without a blocking sort
// to solutions with a blocking sort.
double noSortBonus = epsilon;
if (hasStage(STAGE_SORT_DEFAULT, stats) || hasStage(STAGE_SORT_SIMPLE, stats)) {
noSortBonus = 0;
}
// In the case of ties, prefer single index solutions to ixisect. Index
// intersection solutions are often slower than single-index solutions
// because they require examining a superset of index keys that would be
// examined by a single index scan.
//
// On the other hand, index intersection solutions examine the same
// number or fewer of documents. In the case that index intersection
// allows us to examine fewer documents, the penalty given to ixisect
// can be made up via the no fetch bonus.
double noIxisectBonus = epsilon;
if (hasStage(STAGE_AND_HASH, stats) || hasStage(STAGE_AND_SORTED, stats)) {
noIxisectBonus = 0;
}
const double tieBreakers = noFetchBonus + noSortBonus + noIxisectBonus;
double score = baseScore + productivity + tieBreakers;
log_detail::logScoreFormula([this, stats] { return getProductivityFormula(stats); },
score,
baseScore,
productivity,
noFetchBonus,
noSortBonus,
noIxisectBonus,
tieBreakers);
if (internalQueryForceIntersectionPlans.load()) {
if (hasStage(STAGE_AND_HASH, stats) || hasStage(STAGE_AND_SORTED, stats)) {
// The boost should be >2.001 to make absolutely sure the ixisect plan will win due
// to the combination of 1) productivity, 2) eof bonus, and 3) no ixisect bonus.
score += 3;
log_detail::logScoreBoost(score);
}
}
return score;
}
protected:
/**
* Returns an abstract plan productivity value. Each implementation is free to define the
* formula to calculate the productivity. The value must be withing the range: [0, 1].
*/
virtual double calculateProductivity(const PlanStageStatsType* stats) const = 0;
/**
* Returns a string desribing a formula to calculte plan producivity. It can be used for the log
* output, for example.
*/
virtual std::string getProductivityFormula(const PlanStageStatsType* stats) const = 0;
/**
* Returns the number of advances from the root stage stats, which represents the number of
* documents returned by the PlanStage tree.
*/
virtual double getNumberOfAdvances(const PlanStageStatsType* stats) const = 0;
/**
* True, if the plan stage stats tree represents a plan stage of the given 'type'.
*/
virtual bool hasStage(StageType type, const PlanStageStatsType* stats) const = 0;
};
/**
* A container holding one to-be-scored plan and its associated/relevant data.
* It takes the following template parameters:
* * PlanStageType - the type of plan stages in the execution tree.
* * ResultType - the type of data produced by the execution tree during the candidate plan
* execution.
* * Data - the type of any auxiliary data which is needed to run the execution tree.
*/
template <typename PlanStageType, typename ResultType, typename Data>
struct BaseCandidatePlan {
// A query solution representing this candidate plan.
std::unique_ptr<QuerySolution> solution;
// A root stage of the PlanStage tree constructed from the 'solution'.
PlanStageType root;
// Any auxiliary data required to run the execution tree.
Data data;
// Indicates whether this candidate plan has completed the trial run early by achieving one
// of the trial run metrics.
bool exitedEarly{false};
// If the candidate plan has failed in a recoverable fashion during the trial run, contains a
// non-OK status.
Status status{Status::OK()};
// Any results produced during the plan's execution prior to scoring are retained here.
std::queue<ResultType> results;
// This is used to track the original plan with clean PlanStage tree and the auxiliary data.
// The 'root' and 'data' in this struct could be used to execute trials in multi-planner before
// caching the winning plan, which requires necessary values bound to 'data'. These values
// should not be stored in the plan cache.
boost::optional<std::pair<PlanStageType, Data>> clonedPlan;
};
using CandidatePlan = BaseCandidatePlan<PlanStage*, WorkingSetID, WorkingSet*>;
} // namespace mongo::plan_ranker
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