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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/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"
#include "mongo/db/query/plan_yield_policy.h"
#include "mongo/db/record_id.h"
namespace mongo {
/**
* This stage outputs its mainChild, and possibly it's backup child
* and also updates the cache.
*
* Preconditions: Valid RecordId.
*
* Owns the query solutions and PlanStage roots for all candidate plans.
*/
class MultiPlanStage : public PlanStage {
public:
/**
* Takes no ownership.
*
* If 'shouldCache' is true, writes a cache entry for the winning plan to the plan cache
* when possible. If 'shouldCache' is false, the plan cache will never be written.
*/
MultiPlanStage(OperationContext* txn,
const Collection* collection,
CanonicalQuery* cq,
bool shouldCache = true);
virtual ~MultiPlanStage();
virtual bool isEOF();
virtual StageState work(WorkingSetID* out);
virtual void saveState();
virtual void restoreState(OperationContext* opCtx);
virtual void invalidate(OperationContext* txn, const RecordId& dl, InvalidationType type);
virtual std::vector<PlanStage*> getChildren() const;
virtual StageType stageType() const { return STAGE_MULTI_PLAN; }
virtual PlanStageStats* getStats();
virtual const CommonStats* getCommonStats() const;
virtual const SpecificStats* getSpecificStats() const;
/**
* 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 work(...) will return results from the best plan.
*
* If 'yieldPolicy' is non-NULL, then all locks may be yielded in between round-robin
* works of the candidate plans. By default, 'yieldPolicy' is NULL and no yielding will
* take place.
*
* Returns a non-OK status if the plan was killed during yield.
*/
Status pickBestPlan(PlanYieldPolicy* yieldPolicy);
/**
* Returns the number of times that we are willing to work a plan during a trial period.
*
* Calculated based on a fixed query knob and the size of the collection.
*/
static size_t getTrialPeriodWorks(OperationContext* txn, const Collection* collection);
/**
* Returns the max number of documents which we should allow any plan to return during the
* trial period. As soon as any plan hits this number of documents, the trial period ends.
*/
static size_t getTrialPeriodNumToReturn(const CanonicalQuery& query);
/** 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
*
* The MultiPlanStage retains ownership of the winning QuerySolution and returns an
* unowned pointer.
*/
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. Caller takes ownership of
* all pointers in the returned vector.
*/
std::vector<PlanStageStats*> generateCandidateStats();
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, PlanYieldPolicy* yieldPolicy);
/**
* Checks whether we need to perform either a timing-based yield or a yield for a document
* fetch. If so, then uses 'yieldPolicy' to actually perform the yield.
*
* Returns a non-OK status if killed during a yield.
*/
Status tryYield(PlanYieldPolicy* yieldPolicy);
static const int kNoSuchPlan = -1;
// Not owned here.
OperationContext* _txn;
// Not owned here. Must be non-null.
const Collection* _collection;
// Whether or not we should try to cache the winning plan in the plan cache.
const bool _shouldCache;
// The query that we're trying to figure out the best solution to.
// not owned here
CanonicalQuery* _query;
// Candidate plans. Each candidate includes a child PlanStage tree and QuerySolution which
// are owned here. Ownership of all QuerySolutions is retained here, and will *not* be
// tranferred to the PlanExecutor that wraps this stage.
std::vector<CandidatePlan> _candidates;
// 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;
// Set if this MultiPlanStage cannot continue, and the query must fail. This can happen in
// two ways. The first is that all candidate plans fail. 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.
//
// The second way for failure to occur is that the execution of this query is killed during
// a yield, by some concurrent event such as a collection drop.
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;
// When a stage requests a yield for document fetch, it gives us back a RecordFetcher*
// to use to pull the record into memory. We take ownership of the RecordFetcher here,
// deleting it after we've had a chance to do the fetch. For timing-based yields, we
// just pass a NULL fetcher.
std::unique_ptr<RecordFetcher> _fetcher;
// Stats
CommonStats _commonStats;
MultiPlanStats _specificStats;
};
} // namespace mongo
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