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
|
// @file queryoptimizercursor.h - Interface for a cursor interleaving multiple candidate cursors.
/**
* Copyright (C) 2011 10gen 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/>.
*/
#pragma once
#include "cursor.h"
#include "diskloc.h"
namespace mongo {
class QueryPlan;
class CandidatePlanCharacter;
/**
* An interface for policies overriding the query optimizer's default behavior for selecting
* query plans and creating cursors.
*/
class QueryPlanSelectionPolicy {
public:
virtual ~QueryPlanSelectionPolicy() {}
virtual string name() const = 0;
virtual bool permitOptimalNaturalPlan() const { return true; }
virtual bool permitOptimalIdPlan() const { return true; }
virtual bool permitPlan( const QueryPlan &plan ) const { return true; }
virtual BSONObj planHint( const StringData& ns ) const { return BSONObj(); }
/**
* @return true to request that a created Cursor provide a matcher(). If false, the
* Cursor's matcher() may be NULL if the Cursor can perform accurate query matching
* internally using a non Matcher mechanism. One case where a Matcher might be requested
* even though not strictly necessary to select matching documents is if metadata about
* matches may be requested using MatchDetails. NOTE This is a hint that the Cursor use a
* Matcher, but the hint may be ignored. In some cases the Cursor may not provide
* a Matcher even if 'requestMatcher' is true.
*/
virtual bool requestMatcher() const { return true; }
/**
* @return true to request creating an IntervalBtreeCursor rather than a BtreeCursor when
* possible. An IntervalBtreeCursor is optimized for counting the number of documents
* between two endpoints in a btree. NOTE This is a hint to create an interval cursor, but
* the hint may be ignored. In some cases a different cursor type may be created even if
* 'requestIntervalCursor' is true.
*/
virtual bool requestIntervalCursor() const { return false; }
/** Allow any query plan selection, permitting the query optimizer's default behavior. */
static const QueryPlanSelectionPolicy &any();
/** Prevent unindexed collection scans. */
static const QueryPlanSelectionPolicy &indexOnly();
/**
* Generally hints to use the _id plan, falling back to the $natural plan. However, the
* $natural plan will always be used if optimal for the query.
*/
static const QueryPlanSelectionPolicy &idElseNatural();
private:
class Any;
static Any __any;
class IndexOnly;
static IndexOnly __indexOnly;
class IdElseNatural;
static IdElseNatural __idElseNatural;
};
class QueryPlanSelectionPolicy::Any : public QueryPlanSelectionPolicy {
public:
virtual string name() const { return "any"; }
};
class QueryPlanSelectionPolicy::IndexOnly : public QueryPlanSelectionPolicy {
public:
virtual string name() const { return "indexOnly"; }
virtual bool permitOptimalNaturalPlan() const { return false; }
virtual bool permitPlan( const QueryPlan &plan ) const;
};
class QueryPlanSelectionPolicy::IdElseNatural : public QueryPlanSelectionPolicy {
public:
virtual string name() const { return "idElseNatural"; }
virtual bool permitPlan( const QueryPlan &plan ) const;
virtual BSONObj planHint( const StringData& ns ) const;
};
class FieldRangeSet;
class ExplainQueryInfo;
/**
* Adds functionality to Cursor for running multiple plans, running out of order plans,
* utilizing covered indexes, and generating explain output.
*/
class QueryOptimizerCursor : public Cursor {
public:
/** Candidate plans for the query before it begins running. */
virtual CandidatePlanCharacter initialCandidatePlans() const = 0;
/** FieldRangeSet for the query before it begins running. */
virtual const FieldRangeSet *initialFieldRangeSet() const = 0;
/** @return true if the plan for the current iterate is out of order. */
virtual bool currentPlanScanAndOrderRequired() const = 0;
/** @return true when there may be multiple plans running and some are in order. */
virtual bool runningInitialInOrderPlan() const = 0;
/**
* @return true when some query plans may have been excluded due to plan caching, for a
* non-$or query.
*/
virtual bool hasPossiblyExcludedPlans() const = 0;
/**
* @return true when both in order and out of order candidate plans were available, and
* an out of order candidate plan completed iteration.
*/
virtual bool completePlanOfHybridSetScanAndOrderRequired() const = 0;
/** Clear recorded indexes for the current clause's query patterns. */
virtual void clearIndexesForPatterns() = 0;
/** Stop returning results from out of order plans and do not allow them to complete. */
virtual void abortOutOfOrderPlans() = 0;
/** Note match information for the current iterate, to generate explain output. */
virtual void noteIterate( bool match, bool loadedDocument, bool chunkSkip ) = 0;
/** Note a lock yield for explain output reporting. */
virtual void noteYield() = 0;
/** @return explain output for the query run by this cursor. */
virtual shared_ptr<ExplainQueryInfo> explainQueryInfo() const = 0;
};
} // namespace mongo
|
