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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 <memory>
#include <queue>
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/query/query_planner_params.h"
#include "mongo/db/query/query_solution.h"
#include "mongo/db/record_id.h"
namespace mongo {
class PlanYieldPolicy;
/**
* This stage outputs its mainChild, and possibly its backup child
* and also updates the cache.
*
* Preconditions: Valid RecordId.
*
*/
class CachedPlanStage final : public PlanStage {
public:
CachedPlanStage(OperationContext* opCtx,
Collection* collection,
WorkingSet* ws,
CanonicalQuery* cq,
const QueryPlannerParams& params,
size_t decisionWorks,
PlanStage* root);
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final {
return STAGE_CACHED_PLAN;
}
std::unique_ptr<PlanStageStats> getStats() final;
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
/**
* Runs the cached plan for a trial period, yielding during the trial period according to
* 'yieldPolicy'.
*
* Feedback from the trial period is passed to the plan cache. If the performance is lower
* than expected, the old plan is evicted and a new plan is selected from scratch (again
* yielding according to 'yieldPolicy'). Otherwise, the cached plan is run.
*/
Status pickBestPlan(PlanYieldPolicy* yieldPolicy);
private:
/**
* Passes stats from the trial period run of the cached plan to the plan cache.
*
* If the plan cache entry is deleted before we get a chance to update it, then this
* is a no-op.
*/
void updatePlanCache();
/**
* Uses the QueryPlanner and the MultiPlanStage to re-generate candidate plans for this
* query and select a new winner.
*
* We fallback to a new plan if updatePlanCache() tells us that the performance was worse
* than anticipated during the trial period.
*
* We only modify the plan cache if 'shouldCache' is true.
*/
Status replan(PlanYieldPolicy* yieldPolicy, bool shouldCache);
/**
* May yield during the cached plan stage's trial period or replanning phases.
*
* Returns a non-OK status if query planning fails. In particular, this function returns
* ErrorCodes::QueryPlanKilled if the query plan was killed during a yield, or
* ErrorCodes::MaxTimeMSExpired if the operation exceeded its time limit.
*/
Status tryYield(PlanYieldPolicy* yieldPolicy);
// Not owned. Must be non-null.
Collection* _collection;
// Not owned.
WorkingSet* _ws;
// Not owned.
CanonicalQuery* _canonicalQuery;
QueryPlannerParams _plannerParams;
// The number of work cycles taken to decide on a winning plan when the plan was first
// cached.
size_t _decisionWorks;
// If we fall back to re-planning the query, and there is just one resulting query solution,
// that solution is owned here.
std::unique_ptr<QuerySolution> _replannedQs;
// Any results produced during trial period execution are kept here.
std::queue<WorkingSetID> _results;
// Stats
CachedPlanStats _specificStats;
};
} // namespace mongo
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