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/**
* Copyright (C) 2014 MongoDB 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/>.
*
* 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 GNU Affero General 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/diskloc.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/catalog/collection.h"
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/query/query_solution.h"
#include "mongo/db/query/plan_ranker.h"
namespace mongo {
/**
* This stage outputs its mainChild, and possibly it's backup child
* and also updates the cache.
*
* Preconditions: Valid DiskLoc.
*
*/
class MultiPlanStage : public PlanStage {
public:
/** Takes no ownership */
MultiPlanStage(const Collection* collection, CanonicalQuery* cq);
virtual ~MultiPlanStage();
/**
* Helper used by the destructor to delete losing candidate plans.
*/
void clearCandidates();
virtual bool isEOF();
virtual StageState work(WorkingSetID* out);
virtual void prepareToYield();
virtual void recoverFromYield();
virtual void invalidate(const DiskLoc& dl, InvalidationType type);
virtual std::vector<PlanStage*> getChildren() const;
virtual StageType stageType() const { return STAGE_MULTI_PLAN; }
virtual PlanStageStats* getStats();
/** Takes ownership of QuerySolution and PlanStage. not of WorkingSet */
void addPlan(QuerySolution* solution, PlanStage* root, WorkingSet* sharedWs);
/**
* Runs all plans added by addPlan, ranks them, and picks a best.
* All further calls to getNext(...) will return results from the best plan.
*/
void pickBestPlan();
/** Return true if a best plan has been chosen */
bool bestPlanChosen() const;
/** Return the index of the best plan chosen, for testing */
int bestPlanIdx() const;
/** Returns the QuerySolution for the best plan, or NULL if no best plan */
QuerySolution* bestSolution();
/**
* Returns true if a backup plan was picked.
* This is the case when the best plan has a blocking stage.
* Exposed for testing.
*/
bool hasBackupPlan() const;
//
// Used by explain.
//
/**
* Gathers execution stats for all losing plans.
*/
vector<PlanStageStats*> generateCandidateStats();
/**
* Runs the candidate plans until each has either hit EOF or returned DEAD. Results
* from the plans are thrown out, but execution stats are gathered.
*
* You should call this after calling pickBestPlan(...). It expects that a winning plan
* has already been selected.
*/
Status executeAllPlans();
static const char* kStageType;
private:
//
// Have all our candidate plans do something.
// If all our candidate plans fail, *objOut will contain
// information on the failure.
//
/**
* Calls work on each child plan in a round-robin fashion. We stop when any plan hits EOF
* or returns 'numResults' results.
*
* Returns true if we need to keep working the plans and false otherwise.
*/
bool workAllPlans(size_t numResults);
void allPlansSaveState();
void allPlansRestoreState();
static const int kNoSuchPlan = -1;
// not owned here
const Collection* _collection;
// The query that we're trying to figure out the best solution to.
// not owned here
CanonicalQuery* _query;
// Candidate plans. Owned here.
std::vector<CandidatePlan> _candidates;
// Candidate plans' stats. Owned here.
std::vector<PlanStageStats*> _candidateStats;
// index into _candidates, of the winner of the plan competition
// uses -1 / kNoSuchPlan when best plan is not (yet) known
int _bestPlanIdx;
// index into _candidates, of the backup plan for sort
// uses -1 / kNoSuchPlan when best plan is not (yet) known
int _backupPlanIdx;
// Did all plans fail while we were running them? Note that one plan can fail
// during normal execution of the plan competition. Here is an example:
//
// Plan 1: collection scan with sort. Sort runs out of memory.
// Plan 2: ixscan that provides sort. Won't run out of memory.
//
// We want to choose plan 2 even if plan 1 fails.
bool _failure;
// If everything fails during the plan competition, we can't pick one.
size_t _failureCount;
// if pickBestPlan fails, this is set to the wsid of the statusMember
// returned by ::work()
WorkingSetID _statusMemberId;
// Stats
CommonStats _commonStats;
MultiPlanStats _specificStats;
};
} // namespace mongo
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