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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/>.
*
* 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 <boost/scoped_ptr.hpp>
#include <list>
#include <vector>
#include "mongo/base/status.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/query/plan_ranker.h" // for CandidatePlan
#include "mongo/db/query/runner.h"
#include "mongo/db/query/runner_yield_policy.h"
namespace mongo {
class BSONObj;
class CanonicalQuery;
class DiskLoc;
class PlanExecutor;
class PlanStage;
struct QuerySolution;
class TypeExplain;
struct PlanInfo;
class WorkingSet;
/**
* Runs several plans in parallel and picks the best one. Caches the selection for future use.
*/
class MultiPlanRunner : public Runner {
public:
/**
* Takes ownership of query.
*/
MultiPlanRunner(const Collection* collection, CanonicalQuery* query);
virtual ~MultiPlanRunner();
/**
* Takes ownership of all arguments
*/
void addPlan(QuerySolution* solution, PlanStage* root, WorkingSet* ws);
/**
* Get the next result. Yielding is handled internally. If a best plan is not picked when
* this is called, we call pickBestPlan() internally.
*/
Runner::RunnerState getNext(BSONObj* objOut, DiskLoc* dlOut);
virtual bool isEOF();
/**
* Runs all plans added by addPlan, ranks them, and picks a best. Deletes all loser plans.
* All further calls to getNext(...) will return results from the best plan.
*
* Returns true if a best plan was picked, false if there was an error.
* If there was a failure in the underlying plan, *objOut may hold error details.
*
* If out is not-NULL, set *out to the index of the picked plan.
*/
bool pickBestPlan(size_t* out, BSONObj* objOut);
/**
* 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;
/**
* Caching the best plan is (currently implemented as) a destructive act so we separate it
* from ranking so that inspection of the winning solution is possible. Also sets a backup
* plan if a backup plan is needed. Exposed for testing.
*/
void cacheBestPlan();
virtual void saveState();
virtual bool restoreState();
virtual void invalidate(const DiskLoc& dl, InvalidationType type);
virtual void setYieldPolicy(Runner::YieldPolicy policy);
virtual const std::string& ns();
virtual void kill();
virtual const Collection* collection() { return _collection; }
/**
* Returns OK, allocating and filling in '*explain' and '*planInfo' with details of
* the "winner" plan. Caller takes ownership of '*explain' and '*planInfo'. Otherwise,
* return a status describing the error.
*/
virtual Status getInfo(TypeExplain** explain,
PlanInfo** planInfo) const;
private:
/**
* Have all our candidate plans do something.
* If all our candidate plans fail, *objOut will contain
* information on the failure.
*/
bool workAllPlans(BSONObj* objOut);
void allPlansSaveState();
void allPlansRestoreState();
const Collection* _collection;
// Were we killed by an invalidate?
bool _killed;
// 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;
// We need to cache this so that when we switch from running our candidates to using a
// PlanExecutor, we can set the right yielding policy on it.
Runner::YieldPolicy _policy;
// The winner of the plan competition...
boost::scoped_ptr<PlanExecutor> _bestPlan;
// ...and any results it produced while working toward winning.
std::list<WorkingSetID> _alreadyProduced;
// ...and the solution, for caching.
boost::scoped_ptr<QuerySolution> _bestSolution;
// Candidate plans.
std::vector<CandidatePlan> _candidates;
// Candidate plans' stats. Owned here.
std::vector<PlanStageStats*> _candidateStats;
// Yielding policy we use when we're running candidates.
boost::scoped_ptr<RunnerYieldPolicy> _yieldPolicy;
// The query that we're trying to figure out the best solution to.
boost::scoped_ptr<CanonicalQuery> _query;
// What's the ranking? Produced by pickBestPlan, consumed by cacheBestPlan.
auto_ptr<PlanRankingDecision> _ranking;
// What's the best child? Filled out by pickBestPlan, consumed by cacheBestPlan.
size_t _bestChild;
//
// Backup plan for sort
//
QuerySolution* _backupSolution;
PlanExecutor* _backupPlan;
std::list<WorkingSetID> _backupAlreadyProduced;
};
} // namespace mongo
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