MySQL数据库innodb_rollback_on_timeout参数

在使用MySQL数据库时，有时会出现ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction 这样的报错。而在一个事务中，如果其中一条sql执行时出现此报错，对本事务的其他脚本是否有影响呢，后面如果执行commit操作，报错之前语句的结果是否成功呢？ 这个结果与隔离级别以及innodb_rollback_on_timeout参数设置有关。

注： MySQL默认隔离级别为 REPEATABLE-READ，innodb_rollback_on_timeout为OFF，本文基于innodb表（支持事务）进行测试。

1. 准备工作

1.1  测试环境

MySQL 8.0

1.2 创建测试表及预备数据

创建一张测试表，并插入一条记录

mysql> use testdb;
Database changed
mysql> create table test1(id int primary key,name varchar(20));
Query OK, 0 rows affected (0.01 sec)

mysql> insert into test1 values(1,'1wdrt5');
Query OK, 1 row affected (0.00 sec)

mysql> select  * from  test1;
+----+--------+
| id | name   |
+----+--------+
|  1 | 1wdrt5 |
+----+--------+
1 row in set (0.00 sec)

下面将根据不同的隔离级别及innodb_rollback_on_timeout启停情况进行测试。

2. 测试过程

2.1  隔离级别REPEATABLE-READ &  innodb_rollback_on_timeout =OFF

a) 测试过程：

session A

session B

mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select * from test1 where id=1 for update; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | +----+--------+ 1 row in set (0.00 sec)                                 mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | +----+--------+ 2 rows in set (0.00 sec)

mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select  * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | +----+--------+ 1 row in set (0.00 sec) mysql> insert into test1 values(2,'2edft6'); Query OK, 1 row affected (0.00 sec) mysql> delete from  test1 where id=1; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction mysql> commit; Query OK, 0 rows affected (0.02 sec) mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | +----+--------+ 2 rows in set (0.00 sec)

b） 测试结果：

隔离级别REPEATABLE-READ &  innodb_rollback_on_timeout =OFF （2个参数均为默认值）的情况下，即使事务中有超时回滚报错，超时前的sql不会回滚，依旧执行成功。

2.2   隔离级别为READ-COMMITTED  &  innodb_rollback_on_timeout =OFF

a) 测试过程

session A

session B

mysql> show global variables like 'transaction_isolation'; +-----------------------+----------------+ | Variable_name         | Value          | +-----------------------+----------------+ | transaction_isolation | READ-COMMITTED | +-----------------------+----------------+ 1 row in set (0.01 sec) mysql> use testdb; Database changed mysql> begin ; Query OK, 0 rows affected (0.00 sec) mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | +----+--------+ 2 rows in set (0.00 sec) mysql> select * from test1 where id =1 for update; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | +----+--------+ 1 row in set (0.00 sec)                               mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | +----+--------+ 3 rows in set (0.00 sec)

mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | +----+--------+ 2 rows in set (0.00 sec) mysql> insert into test1 values(3,'3eft6'); Query OK, 1 row affected (0.00 sec) mysql> delete from test1 where id=1; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | +----+--------+ 3 rows in set (0.00 sec)

b）测试结果：

隔离级别为READ-COMMITTED &  innodb_rollback_on_timeout =OFF 情况下，即使事务中有超时回滚报错，超时前的sql不会回滚，依旧执行成功，同2者均为默认值的情况。

2.3  隔离级别REPEATABLE-READ &  innodb_rollback_on_timeout =ON

注： innodb_rollback_on_timeout不能在线修改，需要修改配置文件后重启生效

测试过程：

a) 修改配置文件，重启数据库

在my.cnf文件里添加innodb_rollback_on_timeout=on  再重启数据库即可生效

mysql> show global variables like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
1 row in set (0.00 sec)

mysql> show global variables like 'innodb_rollback_on_timeout';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| innodb_rollback_on_timeout | ON    |
+----------------------------+-------+
1 row in set (0.00 sec)

b) 事务测试过程

session A

session B

mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | +----+--------+ 3 rows in set (0.00 sec) mysql> select * from test1 where id=1 for update; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | +----+--------+ 1 row in set (0.00 sec)                                     mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | +----+--------+ 3 rows in set (0.00 sec)

mysql> use testdb; Database changed mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | +----+--------+ 3 rows in set (0.00 sec) mysql> insert into test1 values(4,'4rgy7'); Query OK, 1 row affected (0.00 sec) mysql> delete from test1 where id=1; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> select * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | +----+--------+ 3 rows in set (0.00 sec)

c) 测试结果：

隔离级别REPEATABLE-READ &  innodb_rollback_on_timeout =ON 的情况下，事务中有超时回滚报错时，超时前sql也会回滚。

2.4   隔离级别为READ-COMMITTED  &  innodb_rollback_on_timeout =ON

a) 参数调整

mysql> set global  transaction_isolation='READ-COMMITTED';
mysql> exit
#  重新登录
mysql> show global variables like 'transaction_isolation';
+-----------------------+----------------+
| Variable_name         | Value          |
+-----------------------+----------------+
| transaction_isolation | READ-COMMITTED |
+-----------------------+----------------+
1 row in set (0.00 sec)

mysql> show global variables like 'innodb_rollback_on_timeout';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| innodb_rollback_on_timeout | ON    |
+----------------------------+-------+
1 row in set (0.00 sec)

b) 测试过程

session A

session B

mysql> use testdb; Database changed mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select  * from  test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | +----+--------+ 3 rows in set (0.00 sec) mysql> select * from test1 where id =1 for  update; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | +----+--------+ 1 row in set (0.00 sec)                               mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> select  * from  test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | |  5 | 5thu8  | +----+--------+ 4 rows in set (0.00 sec)

mysql> use testdb; Database changed mysql> select  * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | +----+--------+ 3 rows in set (0.00 sec) mysql> insert into test1 values(5,'5thu8'); Query OK, 1 row affected (0.01 sec) mysql> delete from test1 where id =1; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> select  * from test1; +----+--------+ | id | name   | +----+--------+ |  1 | 1wdrt5 | |  2 | 2edft6 | |  3 | 3eft6  | |  5 | 5thu8  | +----+--------+ 4 rows in set (0.00 sec)

c)  测试结果

隔离级别为READ-COMMITTED  &  innodb_rollback_on_timeout =ON的情况下，即使事务中有超时回滚报错，超时前的sql不会回滚，依旧执行成功，同2者均为默认值的情况。

3. 小结

在MySQL8.0 中,仅有在隔离级别为READ-COMMITTED  &  innodb_rollback_on_timeout =ON情况下，事务中有超时回滚报错时，超时前sql也会回滚。

隔离级别	innodb_rollback_on_timeout	结果
REPEATABLE-READ	OFF	超时回滚前的SQL不会自动回滚
READ-COMMITTED	OFF	超时回滚前的SQL不会自动回滚
REPEATABLE-READ	ON	超时回滚前的SQL会自动回滚
READ-COMMITTED	ON	超时回滚前的SQL不会自动回滚

TIPS：

1)  测试过程中可以查看information_schema.innodb_trx表观察事务情况，在不同的版本中事务情况不一样.例如，隔离级别REPEATABLE-READ & innodb_rollback_on_timeout=on的情况下，MySQL5.6 中整个事务回滚后会自动创建一个事务，而MySQL5.7则不会再自动创建事务。

2)  在生产环境使用中,建议将innodb_rollback_on_timeout 设置为ON。应用程序一定要做好事务控制，在一个事务出现异常时必须进行显式rollback