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
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
|
/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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 <list>
#include <queue>
#include <vector>
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/record_id.h"
namespace mongo {
class CollatorInterface;
// External params for the merge sort stage. Declared below.
class MergeSortStageParams;
/**
* Merges the outputs of N children, each of which is sorted in the order specified by
* 'pattern'. The output is sorted by 'pattern'. Practically speaking, all of this stage's
* children are indices.
*
* AKA the SERVER-1205 stage. Allows very efficient handling of the following query:
* find($or[{a:1}, {b:1}]).sort({c:1}) with indices {a:1, c:1} and {b:1, c:1}.
*
* Preconditions: For each field in 'pattern' all inputs in the child must handle a
* getFieldDotted for that field.
*/
class MergeSortStage final : public PlanStage {
public:
MergeSortStage(OperationContext* opCtx, const MergeSortStageParams& params, WorkingSet* ws);
void addChild(PlanStage* child);
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final {
return STAGE_SORT_MERGE;
}
std::unique_ptr<PlanStageStats> getStats();
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
private:
struct StageWithValue {
StageWithValue() : id(WorkingSet::INVALID_ID), stage(NULL) {}
WorkingSetID id;
PlanStage* stage;
};
// This stage maintains a priority queue of results from each child stage so that it can quickly
// return the next result according to the sort order. A value in the priority queue is a
// MergingRef, an iterator which refers to a buffered (WorkingSetMember, child stage) pair.
typedef std::list<StageWithValue>::iterator MergingRef;
// The comparison function used in our priority queue.
class StageWithValueComparison {
public:
StageWithValueComparison(WorkingSet* ws, BSONObj pattern, const CollatorInterface* collator)
: _ws(ws), _pattern(pattern), _collator(collator) {}
// Is lhs less than rhs? Note that priority_queue is a max heap by default so we invert
// the return from the expected value.
bool operator()(const MergingRef& lhs, const MergingRef& rhs);
private:
WorkingSet* _ws;
BSONObj _pattern;
const CollatorInterface* _collator;
};
// Not owned by us.
WorkingSet* _ws;
// The pattern that we're sorting by.
BSONObj _pattern;
// Null if this merge sort stage orders strings according to simple binary compare. If non-null,
// represents the collator used to compare strings.
const CollatorInterface* _collator;
// Are we deduplicating on RecordId?
const bool _dedup;
// Which RecordIds have we seen?
stdx::unordered_set<RecordId, RecordId::Hasher> _seen;
// In order to pick the next smallest value, we need each child work(...) until it produces
// a result. This is the queue of children that haven't given us a result yet.
std::queue<PlanStage*> _noResultToMerge;
// The min heap of the results we're returning.
std::priority_queue<MergingRef, std::vector<MergingRef>, StageWithValueComparison> _merging;
// The data referred to by the _merging queue above.
std::list<StageWithValue> _mergingData;
// Stats
MergeSortStats _specificStats;
};
// Parameters that must be provided to a MergeSortStage
class MergeSortStageParams {
public:
MergeSortStageParams() : collator(NULL), dedup(true) {}
// How we're sorting.
BSONObj pattern;
// Null if this merge sort stage orders strings according to simple binary compare. If non-null,
// represents the collator used to compare strings.
const CollatorInterface* collator;
// Do we deduplicate on RecordId?
bool dedup;
};
} // namespace mongo
|
