1. 背景
* InnoDB的表空间可以是共享的或独立的。如果是共享表空间，则所有的表空间都放在一个文件里：ibdata1,ibdata2..ibdataN，这种情况下，目前应该还没办法实现表空间的迁移，除非完全迁移。
* 不管是共享还是独立表空间，InnoDB每个数据表的元数据(metadata)总是保存在 ibdata1 这个共享表空间里，因此该文件必不可少，它还可以用来保存各种数据字典等信息。
* 独立表空间中数据文件单独存放在.ibd文件中。
* MySQL 5.6版本开始支持独立表空间导入与导出。
2. 环境 [ 2台DB实例, MySQL 5.6表迁移至MySQL5.7 ]
* 源实例 MySQL
mysql> show variables like 'innodb%version';
+----------------+--------+
| Variable_name | Value |
+----------------+--------+
| innodb_version | 5.6.36 |
+----------------+--------+
1 row in set (0.01 sec)
mysql> show variables like 'datadir';
+---------------+--------------------+
| Variable_name | Value |
+---------------+--------------------+
| datadir | /data/mysql_data6/ |
+---------------+--------------------+
1 row in set (0.00 sec)* 目的实例 MySQL
mysql> show variables like 'innodb%version';
+----------------+--------+
| Variable_name | Value |
+----------------+--------+
| innodb_version | 5.7.18 |
+----------------+--------+
1 row in set (0.00 sec)
mysql> show variables like 'datadir';
+---------------+--------------------+
| Variable_name | Value |
+---------------+--------------------+
| datadir | /data/mysql_data7/ |
+---------------+--------------------+
1 row in set (0.01 sec)* 源实例 MySQL 迁移的数据库与表信息
mysql> select database();
+------------+
| database() |
+------------+
| mytest |
+------------+
1 row in set (0.00 sec)
mysql> show create table users;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users | CREATE TABLE `users` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
`sex` enum('M','F') NOT NULL DEFAULT 'M',
`age` int(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8mb4 |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)
mysql> select * from users;
+----+-------+-----+-----+
| id | name | sex | age |
+----+-------+-----+-----+
| 1 | tom | M | 25 |
| 2 | jak | F | 38 |
| 3 | sea | M | 43 |
| 4 | lisea | M | 36 |
+----+-------+-----+-----+
4 rows in set (0.00 sec)3. 平滑迁移实战 [ 迁移mytest数据库下users表 ]
* 目的MySQL实例创建相同的数据库与表 [ MySQL 5.7中创建表需要指定row_format=compact ]
mysql> create database mytest character set utf8mb4;
Query OK, 1 row affected (0.03 sec)
mysql> use mytest;
Database changed
mysql> CREATE TABLE `users` (
-> `id` bigint(20) NOT NULL AUTO_INCREMENT,
-> `name` varchar(255) NOT NULL,
-> `sex` enum('M','F') NOT NULL DEFAULT 'M',
-> `age` int(11) NOT NULL DEFAULT '0',
-> PRIMARY KEY (`id`)
-> ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8mb4 row_format=compact;
Query OK, 0 rows affected (0.59 sec)
mysql> system ls -l /data/mysql_data7/mytest/
total 64
-rw-r----- 1 mysql mysql 67 Jul 18 05:21 db.opt
-rw-r----- 1 mysql mysql 8648 Jul 18 05:21 users.frm
-rw-r----- 1 mysql mysql 49152 Jul 18 05:21 users.ibd* 目的MySQL实例丢弃表空间
mysql> alter table users discard tablespace;
Query OK, 0 rows affected (0.01 sec)
mysql> system ls -l /data/mysql_data7/mytest/
total 16
-rw-r----- 1 mysql mysql 67 Jul 18 05:21 db.opt
-rw-r----- 1 mysql mysql 8648 Jul 18 05:21 users.frm* 源MySQL实例刷新表至磁盘并加lock,并且当前表quiesce状态，只读，且创建.cfg metadata文件
mysql> flush tables users for export;
Query OK, 0 rows affected (0.00 sec)* 从源MySQL实例服务止拷贝表文件users.ibd, users.cfg文件至目的MySQL实例中
[root@MySQL ~]# cp -v /data/mysql_data6/mytest/users.{cfg,ibd} /data/mysql_data7/mytest/
`/data/mysql_data6/mytest/users.cfg' -> `/data/mysql_data7/mytest/users.cfg'
`/data/mysql_data6/mytest/users.ibd' -> `/data/mysql_data7/mytest/users.ibd'* 修改目的MySQL实例数据文件下拷贝文件的所有者与所有组
[root@MySQL ~]# chown -v mysql.mysql /data/mysql_data7/mytest/users.{cfg,ibd}
changed ownership of `/data/mysql_data7/mytest/users.cfg' to mysql:mysql
changed ownership of `/data/mysql_data7/mytest/users.ibd' to mysql:mysql* 源MySQL实例释放lock
mysql> unlock tables;
Query OK, 0 rows affected (0.00 sec)* 目的MySQL实例加载表空间
mysql> alter table users import tablespace;
Query OK, 0 rows affected (0.04 sec)* 查看目的MySQL实例表数据 [ MySQL5.6数据成功迁移过来 ]
mysql> select * from users;
+----+-------+-----+-----+
| id | name | sex | age |
+----+-------+-----+-----+
| 1 | tom | M | 25 |
| 2 | jak | F | 38 |
| 3 | sea | M | 43 |
| 4 | lisea | M | 36 |
+----+-------+-----+-----+
4 rows in set (0.00 sec)4. 注意问题
* MySQL 5.6数据迁移到MySQL5.7时，如果创建目的表时不指定row_format，import表数据时会报错，原因在于MySQL 5.6中是Antelope，在MySQL 5.7中是Barracuda，主要是在表压缩和行的动态格式上有所改变。
5. 总结
以需求驱动技术，技术本身没有优略之分，只有业务之分。
