onlineDDL测试

onlineDDL语法：
 alter table
  ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
  ADD   [COLUMN] col_name  column_definition [FIRST|AFTER col_name]
  CHANGE [COLUMN] old_col_name new_col_name column_definition [FIRST|AFTER col_name]
  MODIFY [COLUMN] col_name column_definition
 [FIRST | AFTER col_name],
ALGORITHM [=] {DEFAULT|INPLACE|COPY}  LOCK [=] {DEFAULT|NONE|SHARED|EXCLUSIVE};

简单的说就是原来的语句上，加个ALGORITHM=xxx LOCK=XXXX
ALGORITHM指定了onlineDDL时候是使用COPY,还是INPLACE，
（）COPY表示执行DDL的时候会创建临时表。
（）INPLACE表示不需要创建临时表。（inplace英文单词是原地的意思）
（）DEFAULT表示根据参数old_alter_table来判断是通过INPLACE还是COPY的算法，old_alter_table参数默认为OFF，表示采用INPLACE的方式

LOCK部分为索引创建或删除时对表添加锁的情况，默认是default，可选择的如下：
（）NONE，目标表不添加任何锁，可以进行读写操作，不阻塞任何操作。如果手工指定NONE，但是onlineDDL不支持NONE模式，返回一个错误信息，告诉你用SHARE模式。

（）SHARE，对操作表加一个S锁。不阻塞读操作。写操作会阻塞，将会发生等待MDL锁，如果手工指定SHARE，但是onlineDDL不支持SHARE模式，将返回一个错误信息。

（）EXCLUSIVE，执行索引创建或删除时，对目标表加上一个X锁。读写事务均不能进行。会阻塞所有的线程。这和COPY方式类似，但是不需要像COPY方式那样创建一张临时表。

（）DEFAULT，该模式首先会判断当前操作是否可以使用NONE模式，若不能，则判断是否可以使用SHARE模式，最后判断是否可以使用EXCLUSIVE模式。也就是说DEFAULT会通过判断事务的最大并发性来判断执行DDL的模式。

.创建一个测试表

(mysql5.-)root@localhost [test]> create table ddl_test (id int() not null,name varchar() not null default '',age int() null default ,primary key(id));
Query OK,  rows affected (0.02 sec)

(mysql5.-)root@localhost [test]> 

###这边先看看onlineDDL语法，就是DDL语句后面价格ALGORITHM=INPLACE, lock=none，是否拷贝表，锁模式，什么都没指定默认为defalut
(mysql5.-)root@localhost [test]> ALTER TABLE `ddl_test` MODIFY COLUMN `id`  int() NOT NULL AUTO_INCREMENT FIRST ,ALGORITHM=INPLACE, lock=none;
ERROR  (0A000): ALGORITHM=INPLACE is not supported. Reason: Cannot change column type INPLACE. Try ALGORITHM=COPY.
(mysql5.-)root@localhost [test]> ALTER TABLE `ddl_test` MODIFY COLUMN `id`  int() NOT NULL AUTO_INCREMENT FIRST ,ALGORITHM=copy, lock=none;
ERROR  (0A000): LOCK=NONE is not supported. Reason: COPY algorithm requires a lock. Try LOCK=SHARED.
(mysql5.-)root@localhost [test]> ALTER TABLE `ddl_test` MODIFY COLUMN `id`  int() NOT NULL AUTO_INCREMENT FIRST ,ALGORITHM=copy, lock=shared;
Query OK,  rows affected (0.00 sec)
Records:   Duplicates:   Warnings: 

创建一个大表

(mysql5.-)root@localhost [test]> insert into ddl_test (name,age) select name,age from ddl_test;
Query OK,  rows affected ( min 20.73 sec)
Records:   Duplicates:   Warnings: 

###onlineDDL，前不能针对该表的，有长事务，空闲未提交事务，不然会等待MDL锁 （简单的说，DML 要获取表MDL共享锁，DDL要获取MDL排他锁）
session 

(mysql5.-)root@localhost [test]> select count(name) from ddl_test;

session
(mysql5.-)root@localhost [test]> alter table ddl_test add column address varchar() not null default '',ALGORITHM=INPLACE, lock=none;

session
(mysql5.-)root@localhost [crm]> show processlist;
+----+---------+---------------------+------+---------+------+---------------------------------+------------------------------------------------------------------------------------------------------+
| Id | User    | Host                | db   | Command | Time | State                           | Info                                                                                                 |
+----+---------+---------------------+------+---------+------+---------------------------------+------------------------------------------------------------------------------------------------------+
|  | root    | localhost           | test | Query   |     | optimizing                      | select count(name) from ddl_test                                                                     |
|  | root    | localhost           | test | Query   |     | Waiting for table metadata lock | alter table ddl_test add column address varchar() not null default '',ALGORITHM=INPLACE, lock=non |
|  | root    | localhost           | crm  | Query   |     | starting                        | show processlist                                                                                     |
|  | odstest | 172.16.123.63:  | NULL | Sleep   |   |                                 | NULL                                                                                                 |
|  | odstest | 172.16.123.63:  | test | Sleep   |   |                                 | NULL                                                                                                 |
|  | odstest | 172.16.123.63: | test | Sleep   |   |                                 | NULL                                                                                                 |
|  | odstest | 172.16.123.63:  | test | Sleep   |    |                                 | NULL                                                                                                 |
+----+---------+---------------------+------+---------+------+---------------------------------+------------------------------------------------------------------------------------------------------+
 rows in set (0.00 sec)
在等待MDL锁

.测试onlineDDL

#增加列

session 

(mysql5.-)root@localhost [test]> alter table ddl_test add column address varchar() not null default '',ALGORITHM=INPLACE, lock=none;

session 

(mysql5.-)root@localhost [test]> update ddl_test set name='adfadf' where id> and id <;

session
看到木有，并不阻塞update

(mysql5.-)root@localhost [crm]> show processlist;
+----+---------+---------------------+------+---------+------+----------------+------------------------------------------------------------------------------------------------------+
| Id | User    | Host                | db   | Command | Time | State          | Info                                                                                                 |
+----+---------+---------------------+------+---------+------+----------------+------------------------------------------------------------------------------------------------------+
|  | root    | localhost           | test | Query   |     | updating       | update ddl_test set name='adfadf' where id> and id <                                        |
|  | root    | localhost           | test | Query   |     | altering table | alter table ddl_test add column address varchar() not null default '',ALGORITHM=INPLACE, lock=non |
|  | root    | localhost           | crm  | Query   |     | starting       | show processlist                                                                                     |
|  | odstest | 172.16.123.63:  | NULL | Sleep   |  |                | NULL                                                                                                 |
|  | odstest | 172.16.123.63:  | test | Sleep   |  |                | NULL                                                                                                 |
|  | odstest | 172.16.123.63: | test | Sleep   |  |                | NULL                                                                                                 |
|  | odstest | 172.16.123.63:  | test | Sleep   |   |                | NULL                                                                                                 |
+----+---------+---------------------+------+---------+------+----------------+------------------------------------------------------------------------------------------------------+
 rows in set (0.00 sec)
删除一行数据试试，也不阻塞
(mysql5.-)root@localhost [test]> delete from ddl_test where id=;
Query OK,  row affected (0.02 sec)

(mysql5.-)root@localhost [test]> 

####删除列

session 1
(mysql5.-)root@localhost [test]> alter table ddl_test drop column address,algorithm=inplace,lock=none;
session 2 #### session1--DDL ，执行之后执行。
(mysql5.7-101)root@localhost [test]> select count(name) from ddl_test;
+-------------+
| count(name) |
+-------------+
|    41943040 |
+-------------+
1 row in set (6.99 sec)

session 

(mysql5.-)root@localhost [crm]> show processlist;
+----+---------+---------------------+------+---------+------+----------------+----------------------------------------------------------------------+
| Id | User    | Host                | db   | Command | Time | State          | Info                                                                 |
+----+---------+---------------------+------+---------+------+----------------+----------------------------------------------------------------------+
|  | root    | localhost           | test | Query   |     | optimizing     | select count(name) from ddl_test                                     |
|  | root    | localhost           | test | Query   |    | altering table | alter table ddl_test drop column address,algorithm=inplace,lock=none |
|  | root    | localhost           | crm  | Query   |     | starting       | show processlist                                                     |
|  | odstest | 172.16.123.63:  | NULL | Sleep   |  |                | NULL                                                                 |
|  | odstest | 172.16.123.63:  | test | Sleep   |  |                | NULL                                                                 |
|  | odstest | 172.16.123.63: | test | Sleep   |  |                | NULL                                                                 |
|  | odstest | 172.16.123.63:  | test | Sleep   |   |                | NULL                                                                 |
+----+---------+---------------------+------+---------+------+----------------+----------------------------------------------------------------------+
 rows in set (0.00 sec)

忘记了是DML，删除一行试一下，看会阻塞么，哈哈，并不阻塞（因为表数据很多，执行这个语句，会话二还在执行）
(mysql5.-)root@localhost [test]> delete from ddl_test where id=;
Query OK,  rows affected (0.02 sec)

(mysql5.-)root@localhost [test]>
###

#####修改列
先试一下看看能不能不拷贝表，
(mysql5.-)root@localhost [test]> alter table ddl_test modify column address varchar() not null default '',ALGORITHM=INPLACE, lock=none;
ERROR  (0A000): ALGORITHM=INPLACE is not supported. Reason: Cannot change column type INPLACE. Try ALGORITHM=COPY.
呵呵了，要拷贝表
(mysql5.-)root@localhost [test]> alter table ddl_test modify column address varchar() not null default '',ALGORITHM=copy, lock=none;
那么看看是不是不锁表，也呵呵了，只支持共享锁，那么意味这阻塞DML，不阻塞select
ERROR  (0A000): LOCK=NONE is not supported. Reason: COPY algorithm requires a lock. Try LOCK=SHARED.
(mysql5.-)root@localhost [test]>

小结：只要LOCK模式不是NONE的DDL操作，锁最小范围都是共享锁，意味着还是会阻塞DML，其他情况我就不一一测试了，参考官方手册

问题

####

(mysql5.-)root@localhost [test]> alter table ddl_test add column address varchar() not null default '',ALGORITHM=INPLACE, lock=none;
ERROR  (HY000): Creating index 'FTS_DOC_ID_INDEX' required more than 'innodb_online_alter_log_max_size' bytes of modification log. Please try again.
(mysql5.-)root@localhost [test]> show global variables like 'innodb_online_alter_log_max_size';
+----------------------------------+-----------+
| Variable_name                    | Value     |
+----------------------------------+-----------+
| innodb_online_alter_log_max_size |  |
+----------------------------------+-----------+
 row in set (0.02 sec)
支持动态修改
(mysql5.-)root@localhost [test]>
(mysql5.-)root@localhost [(none)]> set global innodb_online_alter_log_max_size=;
Query OK,  rows affected (0.00 sec)

(mysql5.-)root@localhost [(none)]> 

innodb存储引擎实现Online DDL的原理是在执行创建或者删除操作同时，将DML操作日志写入到一个缓存中，待完成后再将重做应用到表上，以此达到数据的一致性。
这个缓存的大小由参数innodb_online_alter_log_max_size控制，默认大小为128MB,支持动态修改
如果更新的表比较大，并且创建过程中有大量的写操作，如果遇到innodb_online_alter_log_max_size的空间不能存放日志时，会抛出相应的错误，
如果遇到改错误，我们可以调大该参数，以此获得更大的日志缓存空间。还可以设置lock的模式为SHARE，这样在执行过程中会阻塞写操作发生，
因此不需要进行DML日志的记录。

参考资料：

http://dev.mysql.com/doc/refman/5.6/en/innodb-create-index-overview.html