业务需求：

在线修改一张2000W行表的字段长度。

[root@21db01 ~]# pt-online-schema-change –alter=”modify id  VARCHAR(64) CHARSET utf8 COLLATE utf8_general_ci   NOT NULL DEFAULT ‘0’  COMMENT ‘ID’;”  –user=root  –password=XXXX –host=’127.0.0.1′ D=users,t=users_dt  –charset=utf8 –execute –no-check-alter –no-check-replication-filters

Cannot connect to A=utf8,D=users,h=10.1.4.80,p=…,u=root

Cannot connect to A=utf8,D=users,h=10.1.4.82,p=…,u=root

Cannot connect to A=utf8,D=users,h=10.1.6.7,p=…,u=root

Cannot connect to A=utf8,D=users,h=10.1.4.97,p=…,u=root

Cannot connect to A=utf8,D=users,h=10.1.6.8,p=…,u=root

Cannot connect to A=utf8,D=users,h=10.1.4.81,p=…,u=root

Cannot connect to A=utf8,D=users,h=10.1.4.79,p=…,u=root

No slaves found.  See –recursion-method if host 21db01 has slaves.

Not checking slave lag because no slaves were found and –check-slave-lag was not specified.

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 `users`.`users_dt`…

Creating new table…

Created new table users._users_dt_new OK.

Altering new table…

Altered `users`.`_users_dt_new` OK.

2020-09-21T14:17:27 Creating triggers…

2020-09-21T14:17:27 Created triggers OK.

2020-09-21T14:17:27 Copying approximately 26345605 rows…

Copying `users`.`users_dt`:   0% 01:12:38 remain

Copying `users`.`users_dt`:   1% 01:13:24 remain

Copying `users`.`users_dt`:   1% 01:20:53 remain

Copying `users`.`users_dt`:   2% 01:27:24 remain

Copying `users`.`users_dt`:   2% 01:31:22 remain

Copying `users`.`users_dt`:   3% 01:32:27 remain

Copying `users`.`users_dt`:  10% 01:58:39 remain

Copying `users`.`users_dt`:  10% 01:58:30 remain

Copying `users`.`users_dt`:  10% 01:59:12 remain

Copying `users`.`users_dt`:  46% 01:20:35 remain

Copying `users`.`users_dt`:  46% 01:20:22 remain

Copying `users`.`users_dt`:  83% 24:06 remain

Copying `users`.`users_dt`:  98% 01:23 remain

Copying `users`.`users_dt`:  99% 00:37 remain

Copying `users`.`users_dt`:  99% 00:03 remain

2020-09-21T16:49:13 Copied rows OK.

2020-09-21T16:49:13 Analyzing new table…

2020-09-21T16:49:13 Swapping tables…

2020-09-21T16:49:13 Swapped original and new tables OK.

2020-09-21T16:49:13 Dropping old table…

2020-09-21T16:49:50 Dropped old table `users`.`_users_dt_old` OK.

2020-09-21T16:49:50 Dropping triggers…

2020-09-21T16:49:50 Dropped triggers OK.

Successfully altered `users`.`users_dt`.

总共耗时2小时多，普通磁盘。

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