OAK工具ONLINE DDL：
原理：
1. 创建一个临时表，包含DDL所产生的改变。
2. 在原表上创建三个触发器：INSERT, UPDATE, DELETE。
3. COPY原表的数据到临时表，这个时候就算原表有数据也会同时插入到临时表，这样才能保持数据的一致性。
4. 执行RENAME操作：将原表COPY成临时表，新生成的临时表COPY成生产业务表。
5. 删除触发器。
6. 删除临时表。
依赖：
1. 表必须有主键。
2. 在RENAME时不能对表有大的操作。
3. 不要有触发器。
4. 不能删除外键，创建外键。
1. 安装所依赖的软件包：
yum install MySQL-python -y
2. 查看表是否有触发器，如果有则备份后进行删除。如果没有则可以执行下一步。
原因： 因为一个表上一种类型的触发器只能建一个，OAK的工具在ONLINE DDL时是将原表COPY内容到一张临时表，然后通过触发器的方式在上面建三个触发器：
INSERT, UPDATE, DELETE的操作复制到临时表。 因此这里会有冲突。
3. 准备验证脚本：
select sum(crc32(concat(ifnull(id,'NULL'),ifnull(o_id,'NULL')))) as sum from t_test union all select sum(crc32(concat(ifnull(id,'NULL'),ifnull(o_id,'NULL')))) as sum from t_test_new_20140729 ;
脚本的意思： 这个脚本是SUM主键ID的值进行比较，因为表的主键是由自增ID。
4. 执行变更：
python oak-online-alter-table -u root --ask-pass -S /tmp/mysql_3306.sock -d tpcc1000 -t t_test -g t_test_new_20140729 -a "add column name varchar(9) not null default ''" --sleep=300 --skip-delete-pass
-- Connecting to MySQL
Password:
-- Table tpcc1000.t_test is of engine innodb
-- Checking for UNIQUE columns on tpcc1000.t_test, by which to chunk
-- Possible UNIQUE KEY column names in tpcc1000.t_test:
-- - id
-- Table tpcc1000.t_test_new_20140729 has been created
-- Table tpcc1000.t_test_new_20140729 has been altered
-- Checking for UNIQUE columns on tpcc1000.t_test_new_20140729, by which to chunk
-- Possible UNIQUE KEY column names in tpcc1000.t_test_new_20140729:
-- - id
-- Checking for UNIQUE columns on tpcc1000.t_test, by which to chunk
-- - Found following possible unique keys:
-- - id (int)
-- Chosen unique key is 'id'
-- Shared columns: id, o_id
-- Created AD trigger
-- Created AU trigger
-- Created AI trigger
-- Attempting to lock tables
-- Tables locked WRITE
-- id (min, max) values: ([1L], [100000L])
-- Tables unlocked
-- - Reminder: altering tpcc1000.t_test: add column name varchar(9) not...
-- Copying range (1), (1000), progress: 0%
-- + Will sleep for 0.3 seconds
-- Copying range (1000), (2000), progress: 1%
-- + Will sleep for 0.3 seconds
-- Copying range (2000), (3000), progress: 2%
-- + Will sleep for 0.3 seconds
-- Copying range (3000), (4000), progress: 3%
-- + Will sleep for 0.3 seconds
-- Copying range (4000), (5000), progress: 4%
-- + Will sleep for 0.3 seconds
-- Copying range (5000), (6000), progress: 5%
-- + Will sleep for 0.3 seconds
-- Copying range (6000), (7000), progress: 6%
-- + Will sleep for 0.3 seconds
-- Copying range (7000), (8000), progress: 7%
-- + Will sleep for 0.3 seconds
-- Copying range (8000), (9000), progress: 8%
-- + Will sleep for 0.3 seconds
-- Copying range (9000), (10000), progress: 9%
-- + Will sleep for 0.3 seconds
-- Copying range (10000), (11000), progress: 10%
-- + Will sleep for 0.3 seconds
-- Copying range (11000), (12000), progress: 11%
-- + Will sleep for 0.3 seconds
-- Copying range (12000), (13000), progress: 12%
-- + Will sleep for 0.3 seconds
-- Copying range (13000), (14000), progress: 13%
-- + Will sleep for 0.3 seconds
-- Copying range (14000), (15000), progress: 14%
-- + Will sleep for 0.3 seconds
-- Copying range (15000), (16000), progress: 15%
-- + Will sleep for 0.3 seconds
-- Copying range (16000), (17000), progress: 16%
-- + Will sleep for 0.3 seconds
-- Copying range (17000), (18000), progress: 17%
-- + Will sleep for 0.3 seconds
-- Copying range (18000), (19000), progress: 18%
-- + Will sleep for 0.3 seconds
-- Copying range (19000), (20000), progress: 19%
-- + Will sleep for 0.3 seconds
-- - Reminder: altering tpcc1000.t_test: add column name varchar(9) not...
-- Copying range (20000), (21000), progress: 20%
-- + Will sleep for 0.3 seconds
-- Copying range (21000), (22000), progress: 21%
-- + Will sleep for 0.3 seconds
-- Copying range (22000), (23000), progress: 22%
-- + Will sleep for 0.3 seconds
-- Copying range (23000), (24000), progress: 23%
-- + Will sleep for 0.3 seconds
-- Copying range (24000), (25000), progress: 24%
-- + Will sleep for 0.3 seconds
-- Copying range (25000), (26000), progress: 25%
-- + Will sleep for 0.3 seconds
-- Copying range (26000), (27000), progress: 26%
-- + Will sleep for 0.3 seconds
-- Copying range (27000), (28000), progress: 27%
-- + Will sleep for 0.3 seconds
-- Copying range (28000), (29000), progress: 28%
-- + Will sleep for 0.3 seconds
-- Copying range (29000), (30000), progress: 28%
-- + Will sleep for 0.3 seconds
-- Copying range (30000), (31000), progress: 30%
-- + Will sleep for 0.3 seconds
-- Copying range (31000), (32000), progress: 31%
-- + Will sleep for 0.3 seconds
-- Copying range (32000), (33000), progress: 32%
-- + Will sleep for 0.3 seconds
-- Copying range (33000), (34000), progress: 33%
-- + Will sleep for 0.3 seconds
-- Copying range (34000), (35000), progress: 34%
-- + Will sleep for 0.3 seconds
-- Copying range (35000), (36000), progress: 35%
-- + Will sleep for 0.3 seconds
-- Copying range (36000), (37000), progress: 36%
-- + Will sleep for 0.3 seconds
-- Copying range (37000), (38000), progress: 37%
-- + Will sleep for 0.3 seconds
-- Copying range (38000), (39000), progress: 38%
-- + Will sleep for 0.3 seconds
-- Copying range (39000), (40000), progress: 39%
-- + Will sleep for 0.3 seconds
-- - Reminder: altering tpcc1000.t_test: add column name varchar(9) not...
-- Copying range (40000), (41000), progress: 40%
-- + Will sleep for 0.3 seconds
-- Copying range (41000), (42000), progress: 41%
-- + Will sleep for 0.3 seconds
-- Copying range (42000), (43000), progress: 42%
-- + Will sleep for 0.3 seconds
-- Copying range (43000), (44000), progress: 43%
-- + Will sleep for 0.3 seconds
-- Copying range (44000), (45000), progress: 44%
-- + Will sleep for 0.3 seconds
-- Copying range (45000), (46000), progress: 45%
-- + Will sleep for 0.3 seconds
-- Copying range (46000), (47000), progress: 46%
-- + Will sleep for 0.3 seconds
-- Copying range (47000), (48000), progress: 47%
-- + Will sleep for 0.3 seconds
-- Copying range (48000), (49000), progress: 48%
-- + Will sleep for 0.3 seconds
-- Copying range (49000), (50000), progress: 49%
-- + Will sleep for 0.3 seconds
-- Copying range (50000), (51000), progress: 50%
-- + Will sleep for 0.3 seconds
-- Copying range (51000), (52000), progress: 51%
-- + Will sleep for 0.3 seconds
-- Copying range (52000), (53000), progress: 52%
-- + Will sleep for 0.3 seconds
-- Copying range (53000), (54000), progress: 53%
-- + Will sleep for 0.3 seconds
-- Copying range (54000), (55000), progress: 54%
-- + Will sleep for 0.3 seconds
-- Copying range (55000), (56000), progress: 55%
-- + Will sleep for 0.3 seconds
-- Copying range (56000), (57000), progress: 56%
-- + Will sleep for 0.3 seconds
-- Copying range (57000), (58000), progress: 56%
-- + Will sleep for 0.3 seconds
-- Copying range (58000), (59000), progress: 57%
-- + Will sleep for 0.3 seconds
-- Copying range (59000), (60000), progress: 59%
-- + Will sleep for 0.3 seconds
-- - Reminder: altering tpcc1000.t_test: add column name varchar(9) not...
-- Copying range (60000), (61000), progress: 60%
-- + Will sleep for 0.3 seconds
-- Copying range (61000), (62000), progress: 61%
-- + Will sleep for 0.3 seconds
-- Copying range (62000), (63000), progress: 62%
-- + Will sleep for 0.3 seconds
-- Copying range (63000), (64000), progress: 63%
-- + Will sleep for 0.3 seconds
-- Copying range (64000), (65000), progress: 64%
-- + Will sleep for 0.3 seconds
-- Copying range (65000), (66000), progress: 65%
-- + Will sleep for 0.3 seconds
-- Copying range (66000), (67000), progress: 66%
-- + Will sleep for 0.3 seconds
-- Copying range (67000), (68000), progress: 67%
-- + Will sleep for 0.3 seconds
-- Copying range (68000), (69000), progress: 68%
-- + Will sleep for 0.3 seconds
-- Copying range (69000), (70000), progress: 69%
-- + Will sleep for 0.3 seconds
-- Copying range (70000), (71000), progress: 70%
-- + Will sleep for 0.3 seconds
-- Copying range (71000), (72000), progress: 71%
-- + Will sleep for 0.3 seconds
-- Copying range (72000), (73000), progress: 72%
-- + Will sleep for 0.3 seconds
-- Copying range (73000), (74000), progress: 73%
-- + Will sleep for 0.3 seconds
-- Copying range (74000), (75000), progress: 74%
-- + Will sleep for 0.3 seconds
-- Copying range (75000), (76000), progress: 75%
-- + Will sleep for 0.3 seconds
-- Copying range (76000), (77000), progress: 76%
-- + Will sleep for 0.3 seconds
-- Copying range (77000), (78000), progress: 77%
-- + Will sleep for 0.3 seconds
-- Copying range (78000), (79000), progress: 78%
-- + Will sleep for 0.3 seconds
-- Copying range (79000), (80000), progress: 79%
-- + Will sleep for 0.3 seconds
-- - Reminder: altering tpcc1000.t_test: add column name varchar(9) not...
-- Copying range (80000), (81000), progress: 80%
-- + Will sleep for 0.3 seconds
-- Copying range (81000), (82000), progress: 81%
-- + Will sleep for 0.3 seconds
-- Copying range (82000), (83000), progress: 82%
-- + Will sleep for 0.3 seconds
-- Copying range (83000), (84000), progress: 83%
-- + Will sleep for 0.3 seconds
-- Copying range (84000), (85000), progress: 84%
-- + Will sleep for 0.3 seconds
-- Copying range (85000), (86000), progress: 85%
-- + Will sleep for 0.3 seconds
-- Copying range (86000), (87000), progress: 86%
-- + Will sleep for 0.3 seconds
-- Copying range (87000), (88000), progress: 87%
-- + Will sleep for 0.3 seconds
-- Copying range (88000), (89000), progress: 88%
-- + Will sleep for 0.3 seconds
-- Copying range (89000), (90000), progress: 89%
-- + Will sleep for 0.3 seconds
-- Copying range (90000), (91000), progress: 90%
-- + Will sleep for 0.3 seconds
-- Copying range (91000), (92000), progress: 91%
-- + Will sleep for 0.3 seconds
-- Copying range (92000), (93000), progress: 92%
-- + Will sleep for 0.3 seconds
-- Copying range (93000), (94000), progress: 93%
-- + Will sleep for 0.3 seconds
-- Copying range (94000), (95000), progress: 94%
-- + Will sleep for 0.3 seconds
-- Copying range (95000), (96000), progress: 95%
-- + Will sleep for 0.3 seconds
-- Copying range (96000), (97000), progress: 96%
-- + Will sleep for 0.3 seconds
-- Copying range (97000), (98000), progress: 97%
-- + Will sleep for 0.3 seconds
-- Copying range (98000), (99000), progress: 98%
-- + Will sleep for 0.3 seconds
-- Copying range (99000), (100000), progress: 99%
-- + Will sleep for 0.3 seconds
-- Copying range 100% complete. Number of rows: 100000
-- Ghost table creation completed. Note that triggers on tpcc1000.t_test were not removed
这个时候表上的触发器并未删除，原表和临时表都是存在的，因此还需要以下步骤：
5. RENAME临时表回原表，并删除触发器。
(testing)root@localhost [tpcc1000]> use tpcc1000
Database changed
(testing)root@localhost [tpcc1000]> set names utf8;
Query OK, 0 rows affected (0.00 sec)
(testing)root@localhost [tpcc1000]> rename table t_test to t_test_20140729,t_test_new_20140729 to t_test;
Query OK, 0 rows affected (0.00 sec)
注意这一步，一定要放在一个事务里来操作，不然有可能产生程序出错或者数据不一致的情况。
这个执行非常的快， 但也有踩坑的时候， 如果这时有个大查询在原表，或者大的事务在原表上，不管是主库或者从库，在执行这一步时都会DELAY一会，直到获取到锁才会进行操作。
(testing)root@localhost [tpcc1000]> drop trigger t_test_AI_oak;
Query OK, 0 rows affected (0.00 sec)
(testing)root@localhost [tpcc1000]> drop trigger t_test_AU_oak;
Query OK, 0 rows affected (0.00 sec)
(testing)root@localhost [tpcc1000]> drop trigger t_test_AD_oak;
Query OK, 0 rows affected (0.00 sec)
6. 如果原表是有触发器的可以将触发器恢复过来，如果无，删除临时表就结束了。
(testing)root@localhost [tpcc1000]> desc t_test;
+-------+------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+----------------+
| id | int(9) | NO | PRI | NULL | auto_increment |
| o_id | int(11) | NO | | NULL | |
| name | varchar(9) | NO | | | |
+-------+------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
