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
|
/**
* Copyright (C) 2018 MongoDB 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/pipeline/document_source.h"
#include "mongo/executor/task_executor.h"
#include "mongo/s/query/async_results_merger.h"
namespace mongo {
/**
* A stage used only internally to merge results that are being gathered from remote hosts, possibly
* including this host.
*
* Does not assume ownership of cursors until the first call to getNext(). This is to allow this
* stage to be used on mongos without actually iterating the cursors. For example, when this stage
* is parsed on mongos it may later be decided that the merging should happen on one of the shards.
* Then this stage is forwarded to the merging shard, and it should not kill the cursors when it
* goes out of scope on mongos.
*/
class DocumentSourceMergeCursors : public DocumentSource {
public:
static constexpr StringData kStageName = "$mergeCursors"_sd;
/**
* Parses a serialized version of this stage.
*/
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement, const boost::intrusive_ptr<ExpressionContext>&);
/**
* Creates a new DocumentSourceMergeCursors from the given 'remoteCursors'.
*/
static boost::intrusive_ptr<DocumentSource> create(
std::vector<ClusterClientCursorParams::RemoteCursor>&& remoteCursors,
executor::TaskExecutor*,
const boost::intrusive_ptr<ExpressionContext>&);
const char* getSourceName() const final {
return kStageName.rawData();
}
/**
* Absorbs a subsequent $sort if it's merging pre-sorted streams.
*/
Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container);
void detachFromOperationContext() final;
void reattachToOperationContext(OperationContext*) final;
/**
* Serializes this stage to be sent to perform the merging on a different host.
*/
void serializeToArray(
std::vector<Value>& array,
boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
StageConstraints constraints(Pipeline::SplitState pipeState) const final {
StageConstraints constraints(StreamType::kStreaming,
PositionRequirement::kFirst,
HostTypeRequirement::kAnyShard,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed);
constraints.requiresInputDocSource = false;
return constraints;
}
GetNextResult getNext() final;
protected:
void doDispose() final;
private:
DocumentSourceMergeCursors(executor::TaskExecutor*,
std::unique_ptr<ClusterClientCursorParams>,
const boost::intrusive_ptr<ExpressionContext>&);
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final {
MONGO_UNREACHABLE; // Should call serializeToArray instead.
}
executor::TaskExecutor* _executor;
// '_arm' is not populated until the first call to getNext(). If getNext() is never called we
// will not create an AsyncResultsMerger. If we did so the destruction of this stage would cause
// the cursors within the ARM to be killed prematurely. For example, if this stage is parsed on
// mongos then forwarded to the shards, it should not kill the cursors when it goes out of scope
// on mongos.
std::unique_ptr<ClusterClientCursorParams> _armParams;
boost::optional<AsyncResultsMerger> _arm;
};
} // namespace mongo
|
