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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"
namespace mongo {
/**
* A description of a request for a count operation. Copyable.
*/
struct CountRequest {
// Namespace to operate on (e.g. "foo.bar").
std::string ns;
// A predicate describing the set of documents to count.
//
// NOTE:
// Parsing the raw BSON to our AST is left for later so that the parse method does not
// have to look at the catalog. Specifically, creating a CanonicalQuery requires a
// Collection* due to the WhereCallback, and we'd rather not have the parse method require
// a Collection*.
BSONObj query;
// Indicates to the query planner that it should generate a count plan using a
// particular index.
BSONObj hint;
// An integer limiting the number of documents to count.
long long limit;
// An integer indicating to not include the first n documents in the count.
long long skip;
// Whether this is an explain of a count.
bool explain;
};
/**
* Stage used by the count command. This stage sits at the root of a plan tree
* and counts the number of results returned by its child stage.
*
* This should not be confused with the CountScan stage. CountScan is a special
* index access stage which can optimize index access for count operations in
* some cases. On the other hand, *every* count op has a CountStage at its root.
*
* Only returns NEED_TIME until hitting EOF. The count result can be obtained by examining
* the specific stats.
*/
class CountStage : public PlanStage {
public:
CountStage(OperationContext* txn,
Collection* collection,
const CountRequest& request,
WorkingSet* ws,
PlanStage* child);
virtual ~CountStage();
virtual bool isEOF();
virtual StageState work(WorkingSetID* out);
virtual void saveState();
virtual void restoreState(OperationContext* opCtx);
virtual void invalidate(const DiskLoc& dl, InvalidationType type);
virtual std::vector<PlanStage*> getChildren() const;
virtual StageType stageType() const { return STAGE_COUNT; }
PlanStageStats* getStats();
virtual const CommonStats* getCommonStats();
virtual const SpecificStats* getSpecificStats();
static const char* kStageType;
private:
/**
* Computes the count in the case of an empty query, applying the skip and
* limit if necessary. The result is stored in '_specificStats'.
*/
void trivialCount();
// Transactional context for read locks. Not owned by us.
OperationContext* _txn;
// The collection over which we are counting.
Collection* _collection;
CountRequest _request;
// The number of documents that we still need to skip.
long long _leftToSkip;
// The working set used to pass intermediate results between stages. Not owned
// by us.
WorkingSet* _ws;
scoped_ptr<PlanStage> _child;
CommonStats _commonStats;
CountStats _specificStats;
};
} // namespace mongo
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