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
|
/**
* Copyright (C) 2013 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/>.
*
* 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/query/canonical_query.h"
#include "mongo/db/query/index_entry.h"
#include "mongo/db/query/query_solution.h"
namespace mongo {
/**
* Methods for determining what fields and predicates can use indices.
*/
class QueryPlannerIXSelect {
public:
/**
* Return all the fields in the tree rooted at 'node' that we can use an index on
* in order to answer the query.
*
* The 'prefix' argument is a path prefix to be prepended to any fields mentioned in
* predicates encountered. Some array operators specify a path prefix.
*/
static void getFields(const MatchExpression* node,
std::string prefix,
unordered_set<std::string>* out);
/**
* Find all indices prefixed by fields we have predicates over. Only these indices are
* useful in answering the query.
*/
static void findRelevantIndices(const unordered_set<std::string>& fields,
const std::vector<IndexEntry>& indices,
std::vector<IndexEntry>* out);
/**
* Return true if the index key pattern field 'elt' (which belongs to 'index') can be used
* to answer the predicate 'node'.
*
* For example, {field: "hashed"} can only be used with sets of equalities.
* {field: "2d"} can only be used with some geo predicates.
* {field: "2dsphere"} can only be used with some other geo predicates.
*/
static bool compatible(const BSONElement& elt, const IndexEntry& index, MatchExpression* node);
/**
* Determine how useful all of our relevant 'indices' are to all predicates in the subtree
* rooted at 'node'. Affixes a RelevantTag to all predicate nodes which can use an index.
*
* 'prefix' is a path prefix that should be prepended to any path (certain array operators
* imply a path prefix).
*
* For an index to be useful to a predicate, the index must be compatible (see above).
*
* If an index is prefixed by the predicate's path, it's always useful.
*
* If an index is compound but not prefixed by a predicate's path, it's only useful if
* there exists another predicate that 1. will use that index and 2. is related to the
* original predicate by having an AND as a parent.
*/
static void rateIndices(MatchExpression* node,
std::string prefix,
const std::vector<IndexEntry>& indices);
/**
* Amend the RelevantTag lists for all predicates in the subtree rooted at 'node' to remove
* invalid assignments to text and geo indices.
*
* See the body of this function and the specific stripInvalidAssignments functions for details.
*/
static void stripInvalidAssignments(MatchExpression* node,
const std::vector<IndexEntry>& indices);
/**
* In some special cases, we can strip most of the index assignments from the tree early
* on. Specifically, if we find an AND which has a child tagged for equality over a
* single-field unique index, then all other predicate-to-index assignments can be
* stripped off the subtree rooted at 'node'.
*
* This is used to ensure that we always favor key-value lookup plans over any
* more complex plan.
*
* Example:
* Suppose you have match expression OR (AND (a==1, b==2), AND (c==3, d==4)).
* There are indices on fields, 'a', 'b', 'c', and 'd'. The index on 'd' is
* the only unique index.
*
* This code will find that the subtree AND (c==3, d==4) can be answered by
* looking up the value of 'd' in the unique index. Since no better plan than
* a single key lookup is ever available, all assignments in this subtree
* are stripped, except for the assignment of d==4 to the unique 'd' index.
*
* Stripping the assignment for 'c' causes the planner to generate just two
* possible plans:
* 1) an OR of an index scan over 'a' and an index scan over 'd'
* 2) an OR of an index scan over 'b' and an index scan over 'd'
*/
static void stripUnneededAssignments(MatchExpression* node,
const std::vector<IndexEntry>& indices);
private:
/**
* Amend the RelevantTag lists for all predicates in the subtree rooted at 'node' to remove
* invalid assignments to text indexes.
*
* A predicate on a field from a compound text index with a non-empty index prefix
* (e.g. pred {a: 1, b: 1} on index {a: 1, b: 1, c: "text"}) is only considered valid to
* assign to the text index if it is a direct child of an AND with the following properties:
* - it has a TEXT child
* - for every index prefix component, it has an EQ child on that component's path
*
* Note that compatible() enforces the precondition that only EQ nodes are considered
* relevant to text index prefixes.
* If there is a relevant compound text index with a non-empty "index prefix" (e.g. the
* prefix {a: 1, b: 1} for the index {a: 1, b: 1, c: "text"}), amend the RelevantTag(s)
* created above to remove assignments to the text index where the query does not have
* predicates over each indexed field of the prefix.
*
* This is necessary because text indices do not obey the normal rules of sparseness, in
* that they generate no index keys for documents without indexable text data in at least
* one text field (in fact, text indices ignore the sparse option entirely). For example,
* given the text index {a: 1, b: 1, c: "text"}:
*
* - Document {a: 1, b: 6, c: "hello world"} generates 2 index keys
* - Document {a: 1, b: 7, c: {d: 1}} generates 0 index keys
* - Document {a: 1, b: 8} generates 0 index keys
*
* As a result, the query {a: 1} *cannot* be satisfied by the text index {a: 1, b: 1, c:
* "text"}, since documents without indexed text data would not be returned by the query.
* rateIndices() above will eagerly annotate the pred {a: 1} as relevant to the text index;
* those annotations get removed here.
*/
static void stripInvalidAssignmentsToTextIndexes(MatchExpression* node,
const std::vector<IndexEntry>& indices);
/**
* For V1 2dsphere indices we ignore the sparse option. As such we can use an index
* like {nongeo: 1, geo: "2dsphere"} to answer queries only involving nongeo.
*
* For V2 2dsphere indices also ignore the sparse flag but indexing behavior as compared to
* V1 is different. If all of the geo fields are missing from the document we do not index
* it. As such we cannot use V2 sparse indices unless we have a predicate over a geo
* field.
*
* 2dsphere indices V2 are "geo-sparse." That is, if there aren't any geo-indexed fields in
* a document it won't be indexed. As such we can't use an index like {foo:1, geo:
* "2dsphere"} to answer a query on 'foo' if the index is V2 as it will not contain the
* document {foo:1}.
*
* We *can* use it to answer a query on 'foo' if the predicate on 'foo' is AND-related to a
* predicate on every geo field in the index.
*/
static void stripInvalidAssignmentsTo2dsphereIndices(MatchExpression* node,
const std::vector<IndexEntry>& indices);
};
} // namespace mongo
|
