MySQL 8.0.29
Source Code Documentation
record_buffer.h
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1#ifndef RECORD_BUFFER_INCLUDED
2#define RECORD_BUFFER_INCLUDED
3
4/*
5 Copyright (c) 2016, 2021, 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
28#include <assert.h>
29#include "my_base.h" // ha_rows
30
31/**
32 This class represents a buffer that can be used for multi-row reads. It is
33 allocated by the executor and given to the storage engine through the
34 handler, using handler::ha_set_record_buffer(), so that the storage engine
35 can fill the buffer with multiple rows in a single read call.
36
37 For now, the record buffer is only used internally by the storage engine as
38 a prefetch cache. The storage engine fills the record buffer when the
39 executor requests the first record, but it returns a single record only to
40 the executor. If the executor wants to access the records in the buffer, it
41 has to call a handler function such as handler::ha_index_next() or
42 handler::ha_rnd_next(). Then the storage engine will copy the next record
43 from the record buffer to the memory area specified in the arguments of the
44 handler function, typically TABLE::record[0].
45*/
47 /// The maximum number of records that can be stored in the buffer.
49 /// The number of bytes available for each record.
51 /// The number of records currently stored in the buffer.
53 /// The @c uchar buffer that holds the records.
55 /// Tells if end-of-range was found while filling the buffer.
56 bool m_out_of_range = false;
57
58 public:
59 /**
60 Create a new record buffer with the specified size.
61
62 @param records the number of records that can be stored in the buffer
63 @param record_size the size of each record
64 @param buffer the @c uchar buffer that will hold the records (its
65 size should be at least
66 `Record_buffer::buffer_size(records, record_size)`)
67 */
70
71 /**
72 This function calculates how big the @c uchar buffer provided to
73 Record_buffer's constructor must be, given a number of records and
74 the record size.
75
76 @param records the maximum number of records in the buffer
77 @param record_size the size of each record
78 @return the total number of bytes needed for all the records
79 */
80 static constexpr size_t buffer_size(ha_rows records, size_t record_size) {
81 return static_cast<size_t>(records * record_size);
82 }
83
84 /**
85 Get the number of records that can be stored in the buffer.
86 @return the maximum number of records in the buffer
87 */
88 ha_rows max_records() const { return m_max_records; }
89
90 /**
91 Get the amount of space allocated for each record in the buffer.
92 @return the record size
93 */
94 size_t record_size() const { return m_record_size; }
95
96 /**
97 Get the number of records currently stored in the buffer.
98 @return the number of records stored in the buffer
99 */
100 ha_rows records() const { return m_count; }
101
102 /**
103 Get the buffer that holds the record on position @a pos.
104 @param pos the record number (must be smaller than records())
105 @return the @c uchar buffer that holds the specified record
106 */
108 assert(pos < max_records());
109 return m_buffer + m_record_size * pos;
110 }
111
112 /**
113 Add a new record at the end of the buffer.
114 @return the @c uchar buffer of the added record
115 */
117 assert(m_count < max_records());
118 return record(m_count++);
119 }
120
121 /**
122 Remove the record that was last added to the buffer.
123 */
124 void remove_last() {
125 assert(m_count > 0);
126 --m_count;
127 }
128
129 /**
130 Clear the buffer. Remove all the records. The end-of-range flag is
131 preserved.
132 */
133 void clear() { m_count = 0; }
134
135 /**
136 Reset the buffer. Remove all records and clear the end-of-range flag.
137 */
138 void reset() {
139 m_count = 0;
140 set_out_of_range(false);
141 }
142
143 /**
144 Set whether the end of the range was reached while filling the buffer.
145 @param val true if end of range was reached, false if still within range
146 */
147 void set_out_of_range(bool val) { m_out_of_range = val; }
148
149 /**
150 Check if the end of the range was reached while filling the buffer.
151 @retval true if the end range was reached
152 @retval false if the scan is still within the range
153 */
154 bool is_out_of_range() const { return m_out_of_range; }
155};
156
157#endif /* RECORD_BUFFER_INCLUDED */
This class represents a buffer that can be used for multi-row reads.
Definition: record_buffer.h:46
ha_rows m_count
The number of records currently stored in the buffer.
Definition: record_buffer.h:52
void clear()
Clear the buffer.
Definition: record_buffer.h:133
ha_rows m_max_records
The maximum number of records that can be stored in the buffer.
Definition: record_buffer.h:48
static constexpr size_t buffer_size(ha_rows records, size_t record_size)
This function calculates how big the uchar buffer provided to Record_buffer's constructor must be,...
Definition: record_buffer.h:80
uchar * record(ha_rows pos) const
Get the buffer that holds the record on position pos.
Definition: record_buffer.h:107
size_t record_size() const
Get the amount of space allocated for each record in the buffer.
Definition: record_buffer.h:94
void set_out_of_range(bool val)
Set whether the end of the range was reached while filling the buffer.
Definition: record_buffer.h:147
size_t m_record_size
The number of bytes available for each record.
Definition: record_buffer.h:50
ha_rows max_records() const
Get the number of records that can be stored in the buffer.
Definition: record_buffer.h:88
void reset()
Reset the buffer.
Definition: record_buffer.h:138
ha_rows records() const
Get the number of records currently stored in the buffer.
Definition: record_buffer.h:100
bool m_out_of_range
Tells if end-of-range was found while filling the buffer.
Definition: record_buffer.h:56
bool is_out_of_range() const
Check if the end of the range was reached while filling the buffer.
Definition: record_buffer.h:154
uchar * add_record()
Add a new record at the end of the buffer.
Definition: record_buffer.h:116
uchar * m_buffer
The uchar buffer that holds the records.
Definition: record_buffer.h:54
void remove_last()
Remove the record that was last added to the buffer.
Definition: record_buffer.h:124
Record_buffer(ha_rows records, size_t record_size, uchar *buffer)
Create a new record buffer with the specified size.
Definition: record_buffer.h:68
char * pos
Definition: do_ctype.cc:76
This file includes constants used by all storage engines.
my_off_t ha_rows
Definition: my_base.h:1139
unsigned char uchar
Definition: my_inttypes.h:51
mutable_buffer buffer(void *p, size_t n) noexcept
Definition: buffer.h:391