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
|
/**
* 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 <queue>
#include "mongo/db/exec/requires_all_indices_stage.h"
#include "mongo/db/exec/working_set.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/query/canonical_query.h"
#include "mongo/db/query/query_planner_params.h"
#include "mongo/db/query/query_solution.h"
#include "mongo/db/record_id.h"
namespace mongo {
class PlanYieldPolicy;
/**
* Runs a trial period in order to evaluate the cost of a cached plan. If the cost is unexpectedly
* high, the plan cache entry is deactivated and we use multi-planning to select an entirely new
* winning plan. This process is called "replanning".
*
* This stage requires all indices to stay intact during the trial period so that replanning can
* occur with the set of indices in 'params'. As a future improvement, we could instead refresh the
* list of indices in 'params' prior to replanning, and thus avoid inheriting from
* RequiresAllIndicesStage.
*/
class CachedPlanStage final : public RequiresAllIndicesStage {
public:
CachedPlanStage(ExpressionContext* expCtx,
const Collection* collection,
WorkingSet* ws,
CanonicalQuery* cq,
const QueryPlannerParams& params,
size_t decisionWorks,
std::unique_ptr<PlanStage> root);
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final {
return STAGE_CACHED_PLAN;
}
std::unique_ptr<PlanStageStats> getStats() final;
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
/**
* Runs the cached plan for a trial period, yielding during the trial period according to
* 'yieldPolicy'.
*
* Feedback from the trial period is passed to the plan cache. If the performance is lower
* than expected, the old plan is evicted and a new plan is selected from scratch (again
* yielding according to 'yieldPolicy'). Otherwise, the cached plan is run.
*/
Status pickBestPlan(PlanYieldPolicy* yieldPolicy);
private:
/**
* Uses the QueryPlanner and the MultiPlanStage to re-generate candidate plans for this
* query and select a new winner.
*
* We fallback to a new plan if updatePlanCache() tells us that the performance was worse
* than anticipated during the trial period.
*
* We only modify the plan cache if 'shouldCache' is true.
*/
Status replan(PlanYieldPolicy* yieldPolicy, bool shouldCache, std::string reason);
/**
* May yield during the cached plan stage's trial period or replanning phases.
*
* 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 exceeded its time limit.
*/
Status tryYield(PlanYieldPolicy* yieldPolicy);
// Not owned.
WorkingSet* _ws;
// Not owned.
CanonicalQuery* _canonicalQuery;
QueryPlannerParams _plannerParams;
// The number of work cycles taken to decide on a winning plan when the plan was first
// cached.
size_t _decisionWorks;
// If we fall back to re-planning the query, and there is just one resulting query solution,
// that solution is owned here.
std::unique_ptr<QuerySolution> _replannedQs;
// Any results produced during trial period execution are kept here.
std::queue<WorkingSetID> _results;
// Stats
CachedPlanStats _specificStats;
};
} // namespace mongo
|
