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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 "mongo/db/exec/plan_stage.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/matcher/expression.h"
#include "mongo/db/record_id.h"
namespace mongo {
/**
* This stage turns a RecordId into a BSONObj.
*
* In WorkingSetMember terms, it transitions from LOC_AND_IDX to LOC_AND_UNOWNED_OBJ by reading
* the record at the provided loc. Returns verbatim any data that already has an object.
*
* Preconditions: Valid RecordId.
*/
class FetchStage : public PlanStage {
public:
FetchStage(OperationContext* txn,
WorkingSet* ws,
PlanStage* child,
const MatchExpression* filter,
const Collection* collection);
virtual ~FetchStage();
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_FETCH; }
PlanStageStats* getStats();
virtual const CommonStats* getCommonStats();
virtual const SpecificStats* getSpecificStats();
static const char* kStageType;
private:
/**
* If the member (with id memberID) passes our filter, set *out to memberID and return that
* ADVANCED. Otherwise, free memberID and return NEED_TIME.
*/
StageState returnIfMatches(WorkingSetMember* member, WorkingSetID memberID,
WorkingSetID* out);
OperationContext* _txn;
// Collection which is used by this stage. Used to resolve record ids retrieved by child
// stages. The lifetime of the collection must supersede that of the stage.
const Collection* _collection;
// _ws is not owned by us.
WorkingSet* _ws;
scoped_ptr<PlanStage> _child;
// The filter is not owned by us.
const MatchExpression* _filter;
// If we want to return a RecordId and it points to something that's not in memory,
// we return a "please page this in" result. We add a RecordFetcher given back to us by the
// storage engine to the WSM. The RecordFetcher is used by the PlanExecutor when it handles
// the fetch request.
//
// Some stages which request fetches don't need to use '_idBeingPagedIn' (e.g.,
// CollectionScan) because they are implemented with an underlying iterator which keeps
// track of the next WSM to be returned. A FetchStage has no such iterator, but rather
// streams its results from the child. Therefore, when it requests a yield via NEED_FETCH,
// the current WSM must be saved so that the fetched result can be returned on the next
// call to work(). This also requires special invalidation handling not found in stages like
// CollectionScan for when '_idBeingPagedIn' is invalidated before it can be returned.
WorkingSetID _idBeingPagedIn;
// Stats
CommonStats _commonStats;
FetchStats _specificStats;
};
} // namespace mongo
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