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/**
* Copyright (C) 2013 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#pragma once
#include <queue>
#include <vector>
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/exec/plan_stats.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/query/query_solution.h"
namespace mongo {
struct CandidatePlan;
struct PlanRankingDecision;
/**
* Ranks 2 or more plans.
*/
class PlanRanker {
public:
/**
* Returns index in 'candidates' of which plan is best.
* If 'why' is not NULL, populates it with information relevant to why that plan was picked.
*/
static size_t pickBestPlan(const vector<CandidatePlan>& candidates,
PlanRankingDecision* why);
private:
/**
* Assign the stats tree a 'goodness' score. Used internally.
*/
static double scoreTree(const PlanStageStats& stats);
};
/**
* A container holding one to-be-ranked plan and its associated/relevant data.
* Does not own any of its pointers.
*/
struct CandidatePlan {
CandidatePlan(QuerySolution* s, PlanStage* r, WorkingSet* w)
: solution(s), root(r), ws(w) { }
QuerySolution* solution;
PlanStage* root;
WorkingSet* ws;
// Any results produced during the plan's execution prior to ranking are retained here.
std::queue<WorkingSetID> results;
};
/**
* Information about why a plan was picked to be the best. Data here is placed into the cache
* and used by the CachedPlanRunner to compare expected performance with actual.
*/
struct PlanRankingDecision {
// Owned by us.
PlanStageStats* statsOfWinner;
// TODO: We can place anything we want here. What's useful to the cache? What's useful to
// planning and optimization?
};
} // namespace mongo
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