MySQL 8.0.30
Source Code Documentation
opt_costconstantcache.h
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1#ifndef OPT_COSTCONSTANTCACHE_INCLUDED
2#define OPT_COSTCONSTANTCACHE_INCLUDED
3
4/*
5 Copyright (c) 2014, 2022, Oracle and/or its affiliates.
6
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License, version 2.0,
9 as published by the Free Software Foundation.
10
11 This program is also distributed with certain software (including
12 but not limited to OpenSSL) that is licensed under separate terms,
13 as designated in a particular file or component or in included license
14 documentation. The authors of MySQL hereby grant you an additional
15 permission to link the program and your derivative works with the
16 separately licensed software that they have included with MySQL.
17
18 This program is distributed in the hope that it will be useful,
19 but WITHOUT ANY WARRANTY; without even the implied warranty of
20 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
21 GNU General Public License, version 2.0, for more details.
22
23 You should have received a copy of the GNU General Public License
24 along with this program; if not, write to the Free Software
25 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
26
27#include <assert.h>
28#include <stddef.h>
29
32#include "sql/opt_costconstants.h" // Cost_model_constants
33
34/**
35 This class implements a cache for "cost constant sets". This cache
36 is responsible for creating the set of cost constant, giving new
37 sessions access to the latest versions of the cost constants, and
38 for re-reading the cost constant tables in the case where these have
39 been updated.
40
41 The cost constant cache keeps a copy of the current set of cost
42 constants. Each time a new session initializes its Cost_model_server
43 object (by calling Cost_model_server::init() in lex_start()), the
44 Cost_model_server object will request the cost constant cache to
45 give it the current version of the cost constants. This is done by
46 calling Cost_constant_cache::get_cost_constants(). This function
47 will just return a pointer to the current set of cost constants. As
48 time goes, new cost constant sets might be created and added to the
49 cost constant cache. In order to know when a cost constant set can
50 be deleted, reference counting is used. Each time a session asks for
51 the cost constants, the reference counter is incremented. When the
52 session releases the cost constant set by calling
53 @c release_cost_constants(), the reference counter will be
54 decremented. When the reference counter becomes zero, the cost
55 constant set is deleted.
56*/
57
59 public:
60 /**
61 Creates an empty cost constant cache. To initialize it with default
62 cost constants, @c init() must be called. To use cost constants from
63 the cost constant tables, @c reload() must be called.
64 */
66
67 /**
68 Destructor for the cost constant cache. Before the cost constant cache
69 is deleted, @c close() must have been called.
70 */
72
73 /**
74 Initialize the cost module.
75
76 The cost constants will be initialized with the default values found in
77 the source code. To start using the cost constant values found in
78 the configuration tables, the @c reload() function must be called.
79 */
80
81 void init();
82
83 /**
84 Close the cost constant cache.
85
86 All resources owned by the cost constant cache are released.
87 */
88
89 void close();
90
91 /**
92 Reload all cost constants from the configuration tables.
93 */
94
95 void reload();
96
97 /**
98 Get the currently used set of cost constants.
99
100 This function will just return a pointer to a shared version of the
101 cost constants. For tracking of how many sessions that is using the
102 set and to be able to know when it is safe to delete the cost constant
103 object, reference counting is used. This function will increase the
104 ref count for the returned cost constant object. To decrease the reference
105 counter when the cost constants are no longer used,
106 @c release_cost_constants() must be called.
107
108 @note To ensure that the reference counter is only incremented once for
109 each session that uses the cost constant set, this function should only
110 be called once per session.
111
112 @return pointer to the cost constants
113 */
114
117
118 // Increase the ref count on the cost constant object
120
122
124 }
125
126 /**
127 Releases the cost constant set.
128
129 This will decrement the reference counter on the cost constant set and
130 if nobody is using it, it will be deleted. This function should be
131 called each time a client (a session) no longer has any use for a
132 cost constant set that it has previously gotten from calling
133 @c get_cost_constants()
134
135 @param cost_constants pointer to the cost constant set
136 */
137
138 void release_cost_constants(const Cost_model_constants *cost_constants) {
139 assert(cost_constants != nullptr);
140
141 /*
142 The reason for using a const cast here is to be able to keep
143 the cost constant object const outside of this module.
144 */
146 const_cast<Cost_model_constants *>(cost_constants);
147
149
150 const unsigned int ref_count = cost->dec_ref_count();
151
153
154 // If none is using these cost constants then delete them
155 if (ref_count == 0) delete cost;
156 }
157
158 private:
159 /**
160 Create default cost constants.
161
162 This will create cost constants based on default values defined in the
163 source code.
164 */
165
167
168 /**
169 Replace the current cost constants with a new set of cost constants.
170
171 @param new_cost_constants the new cost constants
172 */
173
174 void update_current_cost_constants(Cost_model_constants *new_cost_constants);
175
176 /**
177 The current set of cost constants that will be used by new sessions.
178 */
180
181 /**
182 Mutex protecting the pointer to the current cost constant set and
183 reference counting on all cost constant sets.
184 */
186
188};
189
190/**
191 Initializes the optimizer cost module. This should be done during
192 startup from mysqld.cc.
193*/
194
195void init_optimizer_cost_module(bool enable_plugins);
196
197/**
198 Deletes the optimizer cost module. This should be called when
199 the server stops to release allocated resources.
200*/
201
203
204/**
205 Reloads the optimizer cost constants from the cost constant tables.
206
207 @note In order to read the cost constant tables, a THD is needed. This
208 function will create a new temporary THD that will be used for
209 this. In case the caller already has a THD this will not be used.
210*/
212
213#endif /* OPT_COSTCONSTANTCACHE_INCLUDED */
This class implements a cache for "cost constant sets".
Definition: opt_costconstantcache.h:58
Cost_model_constants * create_defaults() const
Create default cost constants.
Definition: opt_costconstantcache.cc:124
void init()
Initialize the cost module.
Definition: opt_costconstantcache.cc:71
~Cost_constant_cache()
Destructor for the cost constant cache.
Definition: opt_costconstantcache.cc:65
void reload()
Reload all cost constants from the configuration tables.
Definition: opt_costconstantcache.cc:110
bool m_inited
Definition: opt_costconstantcache.h:187
Cost_model_constants * current_cost_constants
The current set of cost constants that will be used by new sessions.
Definition: opt_costconstantcache.h:179
void update_current_cost_constants(Cost_model_constants *new_cost_constants)
Replace the current cost constants with a new set of cost constants.
Definition: opt_costconstantcache.cc:131
mysql_mutex_t LOCK_cost_const
Mutex protecting the pointer to the current cost constant set and reference counting on all cost cons...
Definition: opt_costconstantcache.h:185
const Cost_model_constants * get_cost_constants()
Get the currently used set of cost constants.
Definition: opt_costconstantcache.h:115
void close()
Close the cost constant cache.
Definition: opt_costconstantcache.cc:88
void release_cost_constants(const Cost_model_constants *cost_constants)
Releases the cost constant set.
Definition: opt_costconstantcache.h:138
Cost_constant_cache()
Creates an empty cost constant cache.
Definition: opt_costconstantcache.cc:62
Set of all cost constants used by the server and all storage engines.
Definition: opt_costconstants.h:416
unsigned int dec_ref_count()
Decrement the reference counter for this cost constant set.
Definition: opt_costconstants.h:502
void inc_ref_count()
Increment the reference counter for this cost constant set.
Definition: opt_costconstants.h:491
#define mysql_mutex_lock(M)
Definition: mysql_mutex.h:49
#define mysql_mutex_unlock(M)
Definition: mysql_mutex.h:56
ABI for instrumented mutexes.
void delete_optimizer_cost_module()
Deletes the optimizer cost module.
Definition: opt_costconstantcache.cc:448
void init_optimizer_cost_module(bool enable_plugins)
Initializes the optimizer cost module.
Definition: opt_costconstantcache.cc:437
void reload_optimizer_cost_constants()
Reloads the optimizer cost constants from the cost constant tables.
Definition: opt_costconstantcache.cc:456
Instrumentation helpers for mutexes.
An instrumented mutex structure.
Definition: mysql_mutex_bits.h:49