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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 "mongo/db/exec/plan_stage.h"
#include "mongo/db/query/plan_yield_policy.h"
namespace mongo {
/**
* TrialStage runs a specified 'trial' plan for a given number of iterations, tracking the number of
* times the plan advanced over that duration. If the ratio of advances to works falls below a given
* threshold, then the trial results are discarded and the backup plan is adopted. Otherwise, we
* consider the trial a success, and return the cached results of the trial phase followed by any
* further results that the plan produces.
*
* If the trial plan hits EOF before the trial phase is complete, then it is considered a successful
* trial and the cached results are returned. If the trial plan dies during the trial phase, we
* consider it to have failed and adopt the backup plan instead.
*
* This stage differs from other stages that choose between plans in that it does not evaluate all
* candidates; it evaluates one specific trial plan, and adopts the backup plan if it fails.
* Currently, results from the trial period are discarded on failure. Future use cases may wish to
* extend this class to have multiple policies on what to do in this scenario.
*/
class TrialStage final : public PlanStage {
public:
static const char* kStageType;
/**
* Constructor. Both 'trialPlan' and 'backupPlan' must be non-nullptr; 'maxTrialEWorks' must be
* greater than 0, and 'minWorkAdvancedRatio' must be in the range (0,1].
*/
TrialStage(OperationContext* opCtx,
WorkingSet* ws,
std::unique_ptr<PlanStage> trialPlan,
std::unique_ptr<PlanStage> backupPlan,
size_t maxTrialWorks,
double minWorkAdvancedRatio);
StageState doWork(WorkingSetID* out) final;
// Works the trial plan until the evaluation period is complete.
Status pickBestPlan(PlanYieldPolicy* yieldPolicy);
bool isTrialPhaseComplete() const {
return _specificStats.trialCompleted;
}
bool pickedBackupPlan() const {
return (_specificStats.trialCompleted && !_specificStats.trialSucceeded);
}
StageType stageType() const final {
return STAGE_TRIAL;
}
bool isEOF() final {
return (_specificStats.trialCompleted ? child()->isEOF() : false);
}
const SpecificStats* getSpecificStats() const final {
return &_specificStats;
}
std::unique_ptr<PlanStageStats> getStats() final;
protected:
void doDetachFromOperationContext() final;
void doReattachToOperationContext() final;
void doDispose() final;
private:
void _replaceCurrentPlan(std::unique_ptr<PlanStage>& newPlan);
StageState _workTrialPlan(WorkingSetID* out);
void _assessTrialAndBuildFinalPlan();
std::unique_ptr<PlanStage> _backupPlan;
std::unique_ptr<PlanStage> _queuedData;
TrialStats _specificStats;
WorkingSet* _ws;
};
} // namespace mongo
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