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
|
/**
* 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.
*/
#include "mongo/platform/basic.h"
#include "mongo/base/exact_cast.h"
#include "mongo/db/pipeline/document_source_limit.h"
#include "mongo/db/pipeline/document_source_skip.h"
#include "mongo/db/pipeline/skip_and_limit.h"
#include "mongo/platform/overflow_arithmetic.h"
namespace mongo {
boost::optional<long long> SkipAndLimit::getLimit() const {
return _limit;
}
boost::optional<long long> SkipAndLimit::getSkip() const {
return _skip;
}
SkipThenLimit::SkipThenLimit(boost::optional<long long> skip, boost::optional<long long> limit) {
_skip = skip;
_limit = limit;
}
LimitThenSkip::LimitThenSkip(boost::optional<long long> limit, boost::optional<long long> skip) {
_limit = limit;
// We cannot skip more documents than received after applying limit. So if both limit and skip
// are defined, skip size must be not greater than limit size.
if (skip) {
_skip = std::min(*skip, limit.get_value_or(std::numeric_limits<long long>::max()));
}
}
SkipThenLimit LimitThenSkip::flip() const {
if (_limit) {
return {_skip, *_limit - _skip.get_value_or(0)};
}
return {_skip, boost::none};
}
namespace {
Pipeline::SourceContainer::iterator eraseAndStich(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) {
itr = container->erase(itr);
// If the removed stage wasn't the last in the pipeline, make sure that the stage followed the
// erased stage has a valid pointer to the previous document source.
if (itr != container->end()) {
(*itr)->setSource(itr != container->begin() ? std::prev(itr)->get() : nullptr);
}
return itr;
}
} // namespace
boost::optional<long long> extractLimitForPushdown(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) {
int64_t skipSum = 0;
boost::optional<long long> minLimit;
while (itr != container->end()) {
auto nextStage = itr->get();
auto nextSkip = exact_pointer_cast<DocumentSourceSkip*>(nextStage);
auto nextLimit = exact_pointer_cast<DocumentSourceLimit*>(nextStage);
int64_t safeSum = 0;
// The skip and limit values can be very large, so we need to make sure the sum doesn't
// overflow before applying an optimization to swap the $limit with the $skip.
if (nextSkip && !overflow::add(skipSum, nextSkip->getSkip(), &safeSum)) {
skipSum = safeSum;
++itr;
} else if (nextLimit && !overflow::add(nextLimit->getLimit(), skipSum, &safeSum)) {
if (!minLimit) {
minLimit = safeSum;
} else {
minLimit = std::min(static_cast<long long>(safeSum), *minLimit);
}
itr = eraseAndStich(itr, container);
} else if (!nextStage->constraints().canSwapWithSkippingOrLimitingStage) {
break;
} else {
++itr;
}
}
return minLimit;
}
boost::optional<long long> extractSkipForPushdown(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) {
boost::optional<long long> skipSum;
while (itr != container->end()) {
auto nextStage = itr->get();
auto nextSkip = exact_pointer_cast<DocumentSourceSkip*>(nextStage);
int64_t safeSum = 0;
// The skip values can be very large, so we need to make sure the sum doesn't overflow
// before extracting skip stage for pushdown. Even if we failed to extract $skip stage due
// to overflow, we still want to continue our analysis after it. If there is multiple $skip
// stages one after another, only total sum of skipped documents matters.
if (nextSkip && !overflow::add(skipSum.get_value_or(0), nextSkip->getSkip(), &safeSum)) {
skipSum = safeSum;
itr = eraseAndStich(itr, container);
} else if (!nextSkip && !nextStage->constraints().canSwapWithSkippingOrLimitingStage) {
break;
} else {
++itr;
}
}
return skipSum;
}
} // namespace mongo
|
