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
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
|
/**
* 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 <memory>
#include <string>
#include <vector>
#include "mongo/base/owned_pointer_vector.h"
#include "mongo/base/status.h"
#include "mongo/base/string_data.h"
#include "mongo/db/exec/requires_all_indices_stage.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/query/plan_cache.h"
#include "mongo/db/query/plan_yield_policy.h"
#include "mongo/db/query/query_planner_params.h"
#include "mongo/db/query/query_solution.h"
#include "mongo/db/record_id.h"
#include "mongo/stdx/memory.h"
namespace mongo {
class OperationContext;
/**
* The SubplanStage is used for rooted $or queries. It plans each clause of the $or
* individually, and then creates an overall query plan based on the winning plan from
* each clause.
*
* Uses the MultiPlanStage in order to rank plans for the individual clauses.
*
* Notes on caching strategy:
*
* --Interaction with the plan cache is done on a per-clause basis. For a given clause C,
* if there is a plan in the cache for shape C, then C is planned using the index tags
* obtained from the plan cache entry. If no cached plan is found for C, then a MultiPlanStage
* is used to determine the best plan for the clause; unless there is a tie between multiple
* candidate plans, the winner is inserted into the plan cache and used to plan subsequent
* executions of C. These subsequent executions of shape C could be either as a clause in
* another rooted $or query, or shape C as its own query.
*
* --Plans for entire rooted $or queries are neither written to nor read from the plan cache.
*/
class SubplanStage final : public RequiresAllIndicesStage {
public:
SubplanStage(OperationContext* opCtx,
const Collection* collection,
WorkingSet* ws,
const QueryPlannerParams& params,
CanonicalQuery* cq);
static bool canUseSubplanning(const CanonicalQuery& query);
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final {
return STAGE_SUBPLAN;
}
std::unique_ptr<PlanStageStats> getStats();
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
/**
* Selects a plan using subplanning. First uses the query planning results from
* planSubqueries() and the multi plan stage to select the best plan for each branch.
*
* If this effort fails, then falls back on planning the whole query normally rather
* then planning $or branches independently.
*
* If 'yieldPolicy' is non-NULL, then all locks may be yielded in between round-robin
* works of the candidate plans. By default, 'yieldPolicy' is NULL and no yielding will
* take place.
*
* Returns a non-OK status if query planning fails. In particular, this function returns
* ErrorCodes::QueryPlanKilled if the query plan was killed during a yield, or
* ErrorCodes::MaxTimeMSExpired if the operation has exceeded its time limit.
*/
Status pickBestPlan(PlanYieldPolicy* yieldPolicy);
//
// For testing.
//
/**
* Returns true if the i-th branch was planned by retrieving a cached solution,
* otherwise returns false.
*/
bool branchPlannedFromCache(size_t i) const;
/**
* Provide access to the query solution for our composite solution. Does not relinquish
* ownership.
*/
QuerySolution* compositeSolution() const {
return _compositeSolution.get();
}
private:
/**
* A class used internally in order to keep track of the results of planning
* a particular $or branch.
*/
struct BranchPlanningResult {
BranchPlanningResult(const BranchPlanningResult&) = delete;
BranchPlanningResult& operator=(const BranchPlanningResult&) = delete;
public:
BranchPlanningResult() {}
// A parsed version of one branch of the $or.
std::unique_ptr<CanonicalQuery> canonicalQuery;
// If there is cache data available, then we store it here rather than generating
// a set of alternate plans for the branch. The index tags from the cache data
// can be applied directly to the parent $or MatchExpression when generating the
// composite solution.
std::unique_ptr<CachedSolution> cachedSolution;
// Query solutions resulting from planning the $or branch.
std::vector<std::unique_ptr<QuerySolution>> solutions;
};
/**
* Plan each branch of the $or independently, and store the resulting
* lists of query solutions in '_solutions'.
*
* Called from SubplanStage::make so that construction of the subplan stage
* fails immediately, rather than returning a plan executor and subsequently
* through getNext(...).
*/
Status planSubqueries();
/**
* Uses the query planning results from planSubqueries() and the multi plan stage
* to select the best plan for each branch.
*
* Helper for pickBestPlan().
*/
Status choosePlanForSubqueries(PlanYieldPolicy* yieldPolicy);
/**
* Used as a fallback if subplanning fails. Helper for pickBestPlan().
*/
Status choosePlanWholeQuery(PlanYieldPolicy* yieldPolicy);
// Not owned here.
WorkingSet* _ws;
QueryPlannerParams _plannerParams;
// Not owned here.
CanonicalQuery* _query;
// The copy of the query that we will annotate with tags and use to construct the composite
// solution. Must be a rooted $or query, or a contained $or that has been rewritten to a
// rooted $or.
std::unique_ptr<MatchExpression> _orExpression;
// If we successfully create a "composite solution" by planning each $or branch
// independently, that solution is owned here.
std::unique_ptr<QuerySolution> _compositeSolution;
// Holds a list of the results from planning each branch.
std::vector<std::unique_ptr<BranchPlanningResult>> _branchResults;
// We need this to extract cache-friendly index data from the index assignments.
std::map<IndexEntry::Identifier, size_t> _indexMap;
};
} // namespace mongo
|
