1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
|
/**
* 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/jsobj.h"
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/record_id.h"
namespace mongo {
/**
* This stage implements limit functionality. It only returns 'limit' results before EOF.
*
* Sort has a baked-in limit, as it can optimize the sort if it has a limit.
*
* Preconditions: None.
*/
class LimitStage : public PlanStage {
public:
LimitStage(int limit, WorkingSet* ws, PlanStage* child);
virtual ~LimitStage();
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_LIMIT; }
virtual PlanStageStats* getStats();
virtual const CommonStats* getCommonStats() const;
virtual const SpecificStats* getSpecificStats() const;
static const char* kStageType;
private:
WorkingSet* _ws;
std::unique_ptr<PlanStage> _child;
// We only return this many results.
int _numToReturn;
// Stats
CommonStats _commonStats;
LimitStats _specificStats;
};
} // namespace mongo
|
