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
|
/**
* 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 <string>
#include "mongo/db/commands.h"
#include "mongo/db/commands/map_reduce_command_base.h"
#include "mongo/db/commands/test_commands_enabled.h"
#include "mongo/db/query/query_knobs_gen.h"
#include "mongo/s/commands/cluster_map_reduce.h"
#include "mongo/s/commands/cluster_map_reduce_agg.h"
namespace mongo {
namespace {
/**
* Outline for sharded map reduce for sharded output, $out replace:
*
* ============= mongos =============
* 1. Send map reduce command to all relevant shards with some extra info like the value for
* the chunkSize and the name of the temporary output collection.
*
* ============= shard =============
* 2. Does normal map reduce.
*
* 3. Calls splitVector on itself against the output collection and puts the results into the
* response object.
*
* ============= mongos =============
* 4. If the output collection is *not* sharded, uses the information from splitVector to
* create a pre-split sharded collection.
*
* 5. Grabs the distributed lock for the final output collection.
*
* 6. Sends mapReduce.shardedfinish.
*
* ============= shard =============
* 7. Extracts the list of shards from the mapReduce.shardedfinish and performs a broadcast
* query against all of them to obtain all documents that this shard owns.
*
* 8. Performs the reduce operation against every document from step #7 and outputs them to
* another temporary collection. Also keeps track of the BSONObject size of every "reduced"
* document for each chunk range.
*
* 9. Atomically drops the old output collection and renames the temporary collection to the
* output collection.
*
* ============= mongos =============
* 10. Releases the distributed lock acquired at step #5.
*
* 11. Inspects the BSONObject size from step #8 and determines if it needs to split.
*/
class ClusterMapReduceCommand : public MapReduceCommandBase {
public:
ClusterMapReduceCommand() = default;
AllowedOnSecondary secondaryAllowed(ServiceContext*) const override {
return AllowedOnSecondary::kAlways;
}
bool _runImpl(OperationContext* opCtx,
const std::string& dbname,
const BSONObj& cmd,
std::string& errmsg,
BSONObjBuilder& result) final {
if (getTestCommandsEnabled() && internalQueryUseAggMapReduce.load()) {
return runAggregationMapReduce(opCtx, dbname, cmd, errmsg, result);
}
return runMapReduce(opCtx, dbname, cmd, errmsg, result);
}
} clusterMapReduceCommand;
} // namespace
} // namespace mongo
|
