使用pt-online-schema-change变更数据表某字段长度, 完成后, 查看表结构定义, 却出现了乱码...

数据表zzzz的表结构.

mysql> show create table zzzz \G

*************************** 1. row ***************************

       Table: zzzz

Create Table: CREATE TABLE `zzzz` (

  `id` int(11) NOT NULL AUTO_INCREMENT,

  `name` varchar(10) NOT NULL DEFAULT '' COMMENT '物品名称',

  `category` varchar(10) NOT NULL DEFAULT '' COMMENT '物品分类',

  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='Product infomation'

1 row in set (0.00 sec)

变更字段name的长度为20.

$ pt-online-schema-change --alter "modify name varchar(20) not null default '' comment '物品名称'" --nocheck-replication-filters --recursion-method=processlist h=192.168.4.45,P=3316,u=mha_mgr,p=123456,D=test,t=zzzz --execute

Found 1 slaves:

db02 -> 192.168.4.46:3316

Will check slave lag on:

db02 -> 192.168.4.46:3316

Operation, tries, wait:

  analyze_table, 10, 1

  copy_rows, 10, 0.25

  create_triggers, 10, 1

  drop_triggers, 10, 1

  swap_tables, 10, 1

  update_foreign_keys, 10, 1

Altering `test`.`zzzz`...

Creating new table...

Created new table test._zzzz_new OK.

Waiting forever for new table `test`.`_zzzz_new` to replicate to db02...

Altering new table...

Altered `test`.`_zzzz_new` OK.

2018-01-15T17:31:27 Creating triggers...

2018-01-15T17:31:27 Created triggers OK.

2018-01-15T17:31:27 Copying approximately 1 rows...

2018-01-15T17:31:28 Copied rows OK.

2018-01-15T17:31:28 Analyzing new table...

2018-01-15T17:31:28 Swapping tables...

2018-01-15T17:31:28 Swapped original and new tables OK.

2018-01-15T17:31:28 Dropping old table...

2018-01-15T17:31:28 Dropped old table `test`.`_zzzz_old` OK.

2018-01-15T17:31:28 Dropping triggers...

2018-01-15T17:31:29 Dropped triggers OK.

Successfully altered `test`.`zzzz`.

完成后, 查看表结构, 发现字段的中文注释都成了乱码.

mysql> show create table zzzz \G

*************************** 1. row ***************************

       Table: zzzz

Create Table: CREATE TABLE `zzzz` (

  `id` int(11) NOT NULL AUTO_INCREMENT,

  `name` varchar(20) NOT NULL DEFAULT '' COMMENT '?‰??“??§°',

  `category` varchar(10) NOT NULL DEFAULT '' COMMENT '????',

  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='Product infomation'

1 row in set (0.00 sec)

解决方法, 使用选项--charset(其文档说明: Default character set. If the value is utf8, sets Perl’s binmode on STDOUT to utf8, passes the mysql_enable_utf8 option to DBD::mysql, and runs SET NAMES UTF8 after connecting to MySQL. Any other value sets binmode on STDOUT without the utf8 layer, and runs SET NAMES after connecting to MySQL.), 指明字符集为utf8mb4.

$ pt-online-schema-change --alter "modify name varchar(20) not null default '' comment '物品名称'" --charset=utf8mb4 --nocheck-replication-filters --recursion-method=processlist h=192.168.4.45,P=3316,u=mha_mgr,p=123456,D=test,t=zzzz --execute

瞧, 正常了.

mysql> show create table zzzz \G

*************************** 1. row ***************************

       Table: zzzz

Create Table: CREATE TABLE `zzzz` (

  `id` int(11) NOT NULL AUTO_INCREMENT,

  `name` varchar(20) NOT NULL DEFAULT '' COMMENT '物品名称',

  `category` varchar(10) NOT NULL DEFAULT '' COMMENT '????',

  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='Product infomation'

1 row in set (0.00 sec)

关于pt-online-schema-change工具的更多使用细节, 可参考InnoDB Online DDL续.