摘要：MySQL的存储引擎之EXAMPLE
EXAMPLE是一个不执行任何操作的引擎。它存在的目的是作为MySQL源代码中的一个示例，演示如何编写新的存储引擎。因此，相关的开发人员应该对它最感兴趣。
root@database-one 23:24: [(none)]> show engines; +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | Engine | Support | Comment | Transactions | XA | Savepoints | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES | | MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO | | MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO | | BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO | | MyISAM | YES | MyISAM storage engine | NO | NO | NO | | CSV | YES | CSV storage engine | NO | NO | NO | | ARCHIVE | YES | Archive storage engine | NO | NO | NO | | PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO | | FEDERATED | YES | Federated MySQL storage engine | NO | NO | NO | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ 9 rows in set (0.01 sec)
默认EXAMPLE引擎没有开启，要在从源代码构建MySQL时使用–DWITH_EXAMPLE_STORAGE_ENGINE选项调用CMake开启。笔者这里就不再演示了。
要查看EXAMPLE引擎源代码，请查看MySQL源码的storage/example目录。笔者下载了mysql-5.7.16的源代码。
GongFeideMacBook-Pro-3:Downloads Morinson$ cd mysql-5.7.16
GongFeideMacBook-Pro-3:mysql-5.7.16 Morinson$ ls
BUILD README configure.cmake libevent mysys scripts testclients
CMakeLists.txt VERSION dbug libmysql mysys_ssl sql unittest
COPYING client extra libmysqld packaging sql-common vio
Docs cmake include libservices plugin storage win
Doxyfile-perfschema cmd-line-utils libbinlogevents man rapid strings zlib
INSTALL config.h.cmake libbinlogstandalone mysql-test regex support-files
GongFeideMacBook-Pro-3:mysql-5.7.16 Morinson$ cd storage/
GongFeideMacBook-Pro-3:storage Morinson$ ls
archive csv federated innobase myisammrg partition
blackhole example heap myisam ndb perfschema
GongFeideMacBook-Pro-3:storage Morinson$ cd example/
GongFeideMacBook-Pro-3:example Morinson$ ls -l
total 96
-rw-r--r-- 1 Morinson staff 1079 Sep 29 2016 CMakeLists.txt
-rw-r--r-- 1 Morinson staff 29971 Sep 29 2016 ha_example.cc
-rw-r--r-- 1 Morinson staff 9094 Sep 29 2016 ha_example.h
GongFeideMacBook-Pro-3:example Morinson$ more CMakeLists.txt
# Copyright (c) 2006, 2014, Oracle and/or its affiliates. All rights reserved.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License.
#
# 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
SET(EXAMPLE_PLUGIN_DYNAMIC "ha_example")
SET(EXAMPLE_SOURCES ha_example.cc)
IF(WITH_EXAMPLE_STORAGE_ENGINE AND NOT WITHOUT_EXAMPLE_STORAGE_ENGINE)
MYSQL_ADD_PLUGIN(example ${EXAMPLE_SOURCES} STORAGE_ENGINE DEFAULT)
ELSEIF(NOT WITHOUT_EXAMPLE_STORAGE_ENGINE)
MYSQL_ADD_PLUGIN(example ${EXAMPLE_SOURCES} STORAGE_ENGINE MODULE_ONLY)
ENDIF()
GongFeideMacBook-Pro-3:example Morinson$ more ha_example.h
/* Copyright (c) 2004, 2014, Oracle and/or its affiliates. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
/** @file ha_example.h
@brief
The ha_example engine is a stubbed storage engine for example purposes only;
it does nothing at this point. Its purpose is to provide a source
code illustration of how to begin writing new storage engines; see also
/storage/example/ha_example.cc.
@note
Please read ha_example.cc before reading this file.
Reminder: The example storage engine implements all methods that are *required*
to be implemented. For a full list of all methods that you can implement, see
handler.h.
@see
/sql/handler.h and /storage/example/ha_example.cc
*/
#include "my_global.h" /* ulonglong */
#include "thr_lock.h" /* THR_LOCK, THR_LOCK_DATA */
#include "handler.h" /* handler */
#include "my_base.h" /* ha_rows */
/** @brief
Example_share is a class that will be shared among all open handlers.
This example implements the minimum of what you will probably need.
*/
class Example_share : public Handler_share {
public:
THR_LOCK lock;
Example_share();
~Example_share()
{
thr_lock_delete(&lock);
}
};
/** @brief
Class definition for the storage engine
*/
class ha_example: public handler
{
THR_LOCK_DATA lock; ///< MySQL lock
Example_share *share; ///< Shared lock info
Example_share *get_share(); ///< Get the share
public:
ha_example(handlerton *hton, TABLE_SHARE *table_arg);
~ha_example()
{
}
/** @brief
The name that will be used for display purposes.
*/
const char *table_type() const { return "EXAMPLE"; }
/** @brief
The name of the index type that will be used for display.
Don't implement this method unless you really have indexes.
*/
const char *index_type(uint inx) { return "HASH"; }
/** @brief
The file extensions.
*/
const char **bas_ext() const;
/** @brief
This is a list of flags that indicate what functionality the storage engine
implements. The current table flags are documented in handler.h
*/
ulonglong table_flags() const
{
/*
We are saying that this engine is just statement capable to have
an engine that can only handle statement-based logging. This is
used in testing.
*/
return HA_BINLOG_STMT_CAPABLE;
}
/** @brief
This is a bitmap of flags that indicates how the storage engine
implements indexes. The current index flags are documented in
handler.h. If you do not implement indexes, just return zero here.
@details
part is the key part to check. First key part is 0.
If all_parts is set, MySQL wants to know the flags for the combined
index, up to and including 'part'.
*/
ulong index_flags(uint inx, uint part, bool all_parts) const
{
return 0;
}
/** @brief
unireg.cc will call max_supported_record_length(), max_supported_keys(),
max_supported_key_parts(), uint max_supported_key_length()
to make sure that the storage engine can handle the data it is about to
send. Return *real* limits of your storage engine here; MySQL will do
min(your_limits, MySQL_limits) automatically.
*/
uint max_supported_record_length() const { return HA_MAX_REC_LENGTH; }
/** @brief
unireg.cc will call this to make sure that the storage engine can handle
the data it is about to send. Return *real* limits of your storage engine
here; MySQL will do min(your_limits, MySQL_limits) automatically.
@details
There is no need to implement ..._key_... methods if your engine doesn't
support indexes.
*/
uint max_supported_keys() const { return 0; }
/** @brief
unireg.cc will call this to make sure that the storage engine can handle
the data it is about to send. Return *real* limits of your storage engine
here; MySQL will do min(your_limits, MySQL_limits) automatically.
@details
There is no need to implement ..._key_... methods if your engine doesn't
support indexes.
*/
uint max_supported_key_parts() const { return 0; }
/** @brief
unireg.cc will call this to make sure that the storage engine can handle
the data it is about to send. Return *real* limits of your storage engine
here; MySQL will do min(your_limits, MySQL_limits) automatically.
@details
There is no need to implement ..._key_... methods if your engine doesn't
support indexes.
*/
uint max_supported_key_length() const { return 0; }
/** @brief
Called in test_quick_select to determine if indexes should be used.
*/
virtual double scan_time() { return (double) (stats.records+stats.deleted) / 20.0+10; }
/** @brief
This method will never be called if you do not implement indexes.
*/
virtual double read_time(uint, uint, ha_rows rows)
{ return (double) rows / 20.0+1; }
/*
Everything below are methods that we implement in ha_example.cc.
Most of these methods are not obligatory, skip them and
MySQL will treat them as not implemented
*/
/** @brief
We implement this in ha_example.cc; it's a required method.
*/
int open(const char *name, int mode, uint test_if_locked); // required
/** @brief
We implement this in ha_example.cc; it's a required method.
*/
int close(void); // required
/** @brief
We implement this in ha_example.cc. It's not an obligatory method;
skip it and and MySQL will treat it as not implemented.
*/
int write_row(uchar *buf);
/** @brief
We implement this in ha_example.cc. It's not an obligatory method;
skip it and and MySQL will treat it as not implemented.
*/
int update_row(const uchar *old_data, uchar *new_data);
/** @brief
We implement this in ha_example.cc. It's not an obligatory method;
skip it and and MySQL will treat it as not implemented.
*/
int delete_row(const uchar *buf);
/** @brief
We implement this in ha_example.cc. It's not an obligatory method;
skip it and and MySQL will treat it as not implemented.
*/
int index_read_map(uchar *buf, const uchar *key,
key_part_map keypart_map, enum ha_rkey_function find_flag);
/** @brief
We implement this in ha_example.cc. It's not an obligatory method;
skip it and and MySQL will treat it as not implemented.
*/
int index_next(uchar *buf);
/** @brief
We implement this in ha_example.cc. It's not an obligatory method;
skip it and and MySQL will treat it as not implemented.
*/
int index_prev(uchar *buf);
/** @brief
We implement this in ha_example.cc. It's not an obligatory method;
skip it and and MySQL will treat it as not implemented.
*/
int index_first(uchar *buf);
/** @brief
We implement this in ha_example.cc. It's not an obligatory method;
skip it and and MySQL will treat it as not implemented.
*/
int index_last(uchar *buf);
/** @brief
Unlike index_init(), rnd_init() can be called two consecutive times
without rnd_end() in between (it only makes sense if scan=1). In this
case, the second call should prepare for the new table scan (e.g if
rnd_init() allocates the cursor, the second call should position the
cursor to the start of the table; no need to deallocate and allocate
it again. This is a required method.
*/
int rnd_init(bool scan); //required
int rnd_end();
int rnd_next(uchar *buf); ///< required
int rnd_pos(uchar *buf, uchar *pos); ///< required
void position(const uchar *record); ///< required
int info(uint); ///< required
int extra(enum ha_extra_function operation);
int external_lock(THD *thd, int lock_type); ///< required
int delete_all_rows(void);
int truncate();
ha_rows records_in_range(uint inx, key_range *min_key,
key_range *max_key);
int delete_table(const char *from);
int rename_table(const char * from, const char * to);
int create(const char *name, TABLE *form,
HA_CREATE_INFO *create_info); ///< required
THR_LOCK_DATA **store_lock(THD *thd, THR_LOCK_DATA **to,
enum thr_lock_type lock_type); ///< required
};
GongFeideMacBook-Pro-3:example Morinson$
GongFeideMacBook-Pro-3:example Morinson$ more ha_example.cc
/* Copyright (c) 2004, 2016, Oracle and/or its affiliates. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
/**
@file ha_example.cc
@brief
The ha_example engine is a stubbed storage engine for example purposes only;
it does nothing at this point. Its purpose is to provide a source
code illustration of how to begin writing new storage engines; see also
/storage/example/ha_example.h.
@details
ha_example will let you create/open/delete tables, but
nothing further (for example, indexes are not supported nor can data
be stored in the table). Use this example as a template for
implementing the same functionality in your own storage engine. You
can enable the example storage engine in your build by doing the
following during your build process:<br> ./configure
--with-example-storage-engine
Once this is done, MySQL will let you create tables with:<br>
CREATE TABLE <table name> (...) ENGINE=EXAMPLE;
The example storage engine is set up to use table locks. It
implements an example "SHARE" that is inserted into a hash by table
name. You can use this to store information of state that any
example handler object will be able to see when it is using that
table.
Please read the object definition in ha_example.h before reading the rest
of this file.
@note
When you create an EXAMPLE table, the MySQL Server creates a table .frm
(format) file in the database directory, using the table name as the file
name as is customary with MySQL. No other files are created. To get an idea
of what occurs, here is an example select that would do a scan of an entire
table:
@code
ha_example::store_lock
ha_example::external_lock
......
创建EXAMPLE表时，MySQL将在数据库目录中创建表格式文件，文件以表名开头，扩展名为.frm。不再创建其它文件。表中不能存储任何数据，查询时返回空。
mysql> CREATE TABLE test (i INT) ENGINE = EXAMPLE; Query OK, 0 rows affected (0.78 sec) mysql> INSERT INTO test VALUES(1),(2),(3); ERROR 1031 (HY000): Table storage engine for 'test' doesn't have this option mysql> SELECT * FROM test; Empty set (0.31 sec)
EXAMPLE存储引擎不支持索引。
总的来说，EXAMPLE就是一个给研发人员参考的演示，并不具备任何实际使用价值。
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