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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/exec/plan_cache_util.h"
#include "mongo/db/query/plan_executor.h"
#include "mongo/db/query/plan_ranker.h"
#include "mongo/db/query/sbe_runtime_planner.h"
namespace mongo::sbe {
/**
* Collects execution stats for all candidate plans, ranks them and picks the best.
*
* TODO: add support for backup plan
*/
class MultiPlanner final : public BaseRuntimePlanner {
public:
MultiPlanner(OperationContext* opCtx,
const MultipleCollectionAccessor& collections,
const CanonicalQuery& cq,
const QueryPlannerParams& qpp,
PlanCachingMode cachingMode,
PlanYieldPolicySBE* yieldPolicy)
: BaseRuntimePlanner{opCtx, collections, cq, qpp, yieldPolicy},
_cachingMode{cachingMode},
_maxNumResults{0},
_maxNumReads{0} {}
CandidatePlans plan(
std::vector<std::unique_ptr<QuerySolution>> solutions,
std::vector<std::pair<std::unique_ptr<PlanStage>, stage_builder::PlanStageData>> roots)
final;
private:
struct CandidateCmp {
bool operator()(const plan_ranker::CandidatePlan* lhs,
const plan_ranker::CandidatePlan* rhs) const;
};
using PlanQ = std::priority_queue<plan_ranker::CandidatePlan*,
std::vector<plan_ranker::CandidatePlan*>,
CandidateCmp>;
/**
* Moves candidates into the internal candidates vector, sets up a PlanQ entry for each,
* prepares each candidate's execution tree and tries to fetch the first document to initialize
* plan productivity stats.
*/
PlanQ preparePlans(
const std::vector<size_t>& planIndexes,
size_t trackerResultsBudget,
std::vector<std::unique_ptr<QuerySolution>>& solutions,
std::vector<std::pair<std::unique_ptr<PlanStage>, stage_builder::PlanStageData>>& roots);
/**
* Runs the plans in the queue by fetching one document at a time. Each time the most
* productive plan is executed.
*/
void trialPlans(PlanQ planq);
/**
* Tries to fetch a single document from the plan. Returns true if the trial run should continue
* for the given candidate and false if the trial should end.
*/
bool fetchOneDocument(plan_ranker::CandidatePlan* candidate);
/**
* Executes each plan in to collect execution stats. Stops when all the plans have either:
* * Hit EOF.
* * Returned a pre-defined number of results.
* * Failed
* * Exited early by throwing a special signaling exception.
*
* Each plan is executed at least once. After that plans are executed by fetching one document
* at a time. Every time the most productive plan is executed.
*
* All documents returned by each plan are enqueued into the 'CandidatePlan->results' queue.
*
* Upon completion, returns a vector of candidate plans. Execution stats can be obtained for
* each of the candidate plans by calling 'CandidatePlan->root->getStats()'.
*
* After the trial period ends, plans that ran out of memory or reached EOF are closed.
* All other plans are open, but 'exitedEarly' plans are in an invalid state. Such plans must be
* re-created using the cloned copy before execution of the plan.
*/
std::vector<plan_ranker::CandidatePlan> collectExecutionStats(
std::vector<std::unique_ptr<QuerySolution>> solutions,
std::vector<std::pair<std::unique_ptr<PlanStage>, stage_builder::PlanStageData>> roots,
size_t maxTrialPeriodNumReads);
/**
* Returns the best candidate plan selected according to the plan ranking 'decision'.
*
* Calls 'close' method on all other candidate plans and updates the plan cache entry,
* if possible.
*/
CandidatePlans finalizeExecutionPlans(
std::unique_ptr<mongo::plan_ranker::PlanRankingDecision> decision,
std::vector<plan_ranker::CandidatePlan> candidates) const;
// Describes the cases in which we should write an entry for the winning plan to the plan cache.
const PlanCachingMode _cachingMode;
size_t _maxNumResults;
size_t _maxNumReads;
};
} // namespace mongo::sbe
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